Merge tag 'drivers-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc

Pull ARM SoC driver updates from Arnd Bergmann:
 "These are updates for drivers that are tied to a particular SoC,
  including the correspondig device tree bindings:

   - A couple of reset controller changes for unisoc, uniphier, renesas
     and zte platforms

   - memory controller driver fixes for omap and tegra

   - Rockchip io domain driver updates

   - Lots of updates for qualcomm platforms, mostly touching their
     firmware and power management drivers

   - Tegra FUSE and firmware driver updateѕ

   - Support for virtio transports in the SCMI firmware framework

   - cleanup of ixp4xx drivers, towards enabling multiplatform support
     and bringing it up to date with modern platforms

   - Minor updates for keystone, mediatek, omap, renesas"

* tag 'drivers-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc: (96 commits)
  reset: simple: remove ZTE details in Kconfig help
  soc: rockchip: io-domain: Remove unneeded semicolon
  soc: rockchip: io-domain: add rk3568 support
  dt-bindings: power: add rk3568-pmu-io-domain support
  bus: ixp4xx: return on error in ixp4xx_exp_probe()
  soc: renesas: Prefer memcpy() over strcpy()
  firmware: tegra: Stop using seq_get_buf()
  soc/tegra: fuse: Enable fuse clock on suspend for Tegra124
  soc/tegra: fuse: Add runtime PM support
  soc/tegra: fuse: Clear fuse->clk on driver probe failure
  soc/tegra: pmc: Prevent racing with cpuilde driver
  soc/tegra: bpmp: Remove unused including <linux/version.h>
  dt-bindings: soc: ti: pruss: Add dma-coherent property
  soc: ti: Remove pm_runtime_irq_safe() usage for smartreflex
  soc: ti: pruss: Enable support for ICSSG subsystems on K3 AM64x SoCs
  dt-bindings: soc: ti: pruss: Update bindings for K3 AM64x SoCs
  firmware: arm_scmi: Use WARN_ON() to check configured transports
  firmware: arm_scmi: Fix boolconv.cocci warnings
  soc: mediatek: mmsys: Fix missing UFOE component in mt8173 table routing
  soc: mediatek: mmsys: add MT8365 support
  ...

12 files changed, 1452 insertions, 162 deletions

diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index 5d3fd803d2bb..220a58cf0a44 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -6,39 +6,7 @@
 
 menu "Firmware Drivers"
 
-config ARM_SCMI_PROTOCOL
-	tristate "ARM System Control and Management Interface (SCMI) Message Protocol"
-	depends on ARM || ARM64 || COMPILE_TEST
-	depends on MAILBOX || HAVE_ARM_SMCCC_DISCOVERY
-	help
-	  ARM System Control and Management Interface (SCMI) protocol is a
-	  set of operating system-independent software interfaces that are
-	  used in system management. SCMI is extensible and currently provides
-	  interfaces for: Discovery and self-description of the interfaces
-	  it supports, Power domain management which is the ability to place
-	  a given device or domain into the various power-saving states that
-	  it supports, Performance management which is the ability to control
-	  the performance of a domain that is composed of compute engines
-	  such as application processors and other accelerators, Clock
-	  management which is the ability to set and inquire rates on platform
-	  managed clocks and Sensor management which is the ability to read
-	  sensor data, and be notified of sensor value.
-
-	  This protocol library provides interface for all the client drivers
-	  making use of the features offered by the SCMI.
-
-config ARM_SCMI_POWER_DOMAIN
-	tristate "SCMI power domain driver"
-	depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
-	default y
-	select PM_GENERIC_DOMAINS if PM
-	help
-	  This enables support for the SCMI power domains which can be
-	  enabled or disabled via the SCP firmware
-
-	  This driver can also be built as a module.  If so, the module
-	  will be called scmi_pm_domain. Note this may needed early in boot
-	  before rootfs may be available.
+source "drivers/firmware/arm_scmi/Kconfig"
 
 config ARM_SCPI_PROTOCOL
 	tristate "ARM System Control and Power Interface (SCPI) Message Protocol"
@@ -235,7 +203,7 @@ config INTEL_STRATIX10_RSU
 	  Say Y here if you want Intel RSU support.
 
 config QCOM_SCM
-	bool
+	tristate "Qcom SCM driver"
 	depends on ARM || ARM64
 	depends on HAVE_ARM_SMCCC
 	select RESET_CONTROLLER
diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
index 705fabe88156..5ced0673d94b 100644
--- a/drivers/firmware/Makefile
+++ b/drivers/firmware/Makefile
@@ -17,7 +17,8 @@ obj-$(CONFIG_ISCSI_IBFT)	+= iscsi_ibft.o
 obj-$(CONFIG_FIRMWARE_MEMMAP)	+= memmap.o
 obj-$(CONFIG_RASPBERRYPI_FIRMWARE) += raspberrypi.o
 obj-$(CONFIG_FW_CFG_SYSFS)	+= qemu_fw_cfg.o
-obj-$(CONFIG_QCOM_SCM)		+= qcom_scm.o qcom_scm-smc.o qcom_scm-legacy.o
+obj-$(CONFIG_QCOM_SCM)		+= qcom-scm.o
+qcom-scm-objs += qcom_scm.o qcom_scm-smc.o qcom_scm-legacy.o
 obj-$(CONFIG_SYSFB)		+= sysfb.o
 obj-$(CONFIG_SYSFB_SIMPLEFB)	+= sysfb_simplefb.o
 obj-$(CONFIG_TI_SCI_PROTOCOL)	+= ti_sci.o
diff --git a/drivers/firmware/arm_scmi/Kconfig b/drivers/firmware/arm_scmi/Kconfig
new file mode 100644
index 000000000000..7f4d2435503b
--- /dev/null
+++ b/drivers/firmware/arm_scmi/Kconfig
@@ -0,0 +1,95 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menu "ARM System Control and Management Interface Protocol"
+
+config ARM_SCMI_PROTOCOL
+	tristate "ARM System Control and Management Interface (SCMI) Message Protocol"
+	depends on ARM || ARM64 || COMPILE_TEST
+	help
+	  ARM System Control and Management Interface (SCMI) protocol is a
+	  set of operating system-independent software interfaces that are
+	  used in system management. SCMI is extensible and currently provides
+	  interfaces for: Discovery and self-description of the interfaces
+	  it supports, Power domain management which is the ability to place
+	  a given device or domain into the various power-saving states that
+	  it supports, Performance management which is the ability to control
+	  the performance of a domain that is composed of compute engines
+	  such as application processors and other accelerators, Clock
+	  management which is the ability to set and inquire rates on platform
+	  managed clocks and Sensor management which is the ability to read
+	  sensor data, and be notified of sensor value.
+
+	  This protocol library provides interface for all the client drivers
+	  making use of the features offered by the SCMI.
+
+if ARM_SCMI_PROTOCOL
+
+config ARM_SCMI_HAVE_TRANSPORT
+	bool
+	help
+	  This declares whether at least one SCMI transport has been configured.
+	  Used to trigger a build bug when trying to build SCMI without any
+	  configured transport.
+
+config ARM_SCMI_HAVE_SHMEM
+	bool
+	help
+	  This declares whether a shared memory based transport for SCMI is
+	  available.
+
+config ARM_SCMI_HAVE_MSG
+	bool
+	help
+	  This declares whether a message passing based transport for SCMI is
+	  available.
+
+config ARM_SCMI_TRANSPORT_MAILBOX
+	bool "SCMI transport based on Mailbox"
+	depends on MAILBOX
+	select ARM_SCMI_HAVE_TRANSPORT
+	select ARM_SCMI_HAVE_SHMEM
+	default y
+	help
+	  Enable mailbox based transport for SCMI.
+
+	  If you want the ARM SCMI PROTOCOL stack to include support for a
+	  transport based on mailboxes, answer Y.
+
+config ARM_SCMI_TRANSPORT_SMC
+	bool "SCMI transport based on SMC"
+	depends on HAVE_ARM_SMCCC_DISCOVERY
+	select ARM_SCMI_HAVE_TRANSPORT
+	select ARM_SCMI_HAVE_SHMEM
+	default y
+	help
+	  Enable SMC based transport for SCMI.
+
+	  If you want the ARM SCMI PROTOCOL stack to include support for a
+	  transport based on SMC, answer Y.
+
+config ARM_SCMI_TRANSPORT_VIRTIO
+	bool "SCMI transport based on VirtIO"
+	depends on VIRTIO
+	select ARM_SCMI_HAVE_TRANSPORT
+	select ARM_SCMI_HAVE_MSG
+	help
+	  This enables the virtio based transport for SCMI.
+
+	  If you want the ARM SCMI PROTOCOL stack to include support for a
+	  transport based on VirtIO, answer Y.
+
+endif #ARM_SCMI_PROTOCOL
+
+config ARM_SCMI_POWER_DOMAIN
+	tristate "SCMI power domain driver"
+	depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
+	default y
+	select PM_GENERIC_DOMAINS if PM
+	help
+	  This enables support for the SCMI power domains which can be
+	  enabled or disabled via the SCP firmware
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called scmi_pm_domain. Note this may needed early in boot
+	  before rootfs may be available.
+
+endmenu
diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
index 6a2ef63306d6..1dcf123d64ab 100644
--- a/drivers/firmware/arm_scmi/Makefile
+++ b/drivers/firmware/arm_scmi/Makefile
@@ -1,9 +1,11 @@
 # SPDX-License-Identifier: GPL-2.0-only
 scmi-bus-y = bus.o
 scmi-driver-y = driver.o notify.o
-scmi-transport-y = shmem.o
-scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
-scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
+scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
+scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_MAILBOX) += mailbox.o
+scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_SMC) += smc.o
+scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
+scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO) += virtio.o
 scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
 scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
 		    $(scmi-transport-y)
diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index 8685619d38f9..dea1bfbe1052 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -14,8 +14,12 @@
 #include <linux/device.h>
 #include <linux/errno.h>
 #include <linux/kernel.h>
+#include <linux/hashtable.h>
+#include <linux/list.h>
 #include <linux/module.h>
+#include <linux/refcount.h>
 #include <linux/scmi_protocol.h>
+#include <linux/spinlock.h>
 #include <linux/types.h>
 
 #include <asm/unaligned.h>
@@ -65,11 +69,22 @@ struct scmi_msg_resp_prot_version {
 #define MSG_XTRACT_TOKEN(hdr)	FIELD_GET(MSG_TOKEN_ID_MASK, (hdr))
 #define MSG_TOKEN_MAX		(MSG_XTRACT_TOKEN(MSG_TOKEN_ID_MASK) + 1)
 
+/*
+ * Size of @pending_xfers hashtable included in @scmi_xfers_info; ideally, in
+ * order to minimize space and collisions, this should equal max_msg, i.e. the
+ * maximum number of in-flight messages on a specific platform, but such value
+ * is only available at runtime while kernel hashtables are statically sized:
+ * pick instead as a fixed static size the maximum number of entries that can
+ * fit the whole table into one 4k page.
+ */
+#define SCMI_PENDING_XFERS_HT_ORDER_SZ		9
+
 /**
  * struct scmi_msg_hdr - Message(Tx/Rx) header
  *
  * @id: The identifier of the message being sent
  * @protocol_id: The identifier of the protocol used to send @id message
+ * @type: The SCMI type for this message
  * @seq: The token to identify the message. When a message returns, the
  *	platform returns the whole message header unmodified including the
  *	token
@@ -80,6 +95,7 @@ struct scmi_msg_resp_prot_version {
 struct scmi_msg_hdr {
 	u8 id;
 	u8 protocol_id;
+	u8 type;
 	u16 seq;
 	u32 status;
 	bool poll_completion;
@@ -89,13 +105,14 @@ struct scmi_msg_hdr {
  * pack_scmi_header() - packs and returns 32-bit header
  *
  * @hdr: pointer to header containing all the information on message id,
- *	protocol id and sequence id.
+ *	protocol id, sequence id and type.
  *
  * Return: 32-bit packed message header to be sent to the platform.
  */
 static inline u32 pack_scmi_header(struct scmi_msg_hdr *hdr)
 {
 	return FIELD_PREP(MSG_ID_MASK, hdr->id) |
+		FIELD_PREP(MSG_TYPE_MASK, hdr->type) |
 		FIELD_PREP(MSG_TOKEN_ID_MASK, hdr->seq) |
 		FIELD_PREP(MSG_PROTOCOL_ID_MASK, hdr->protocol_id);
 }
@@ -110,6 +127,7 @@ static inline void unpack_scmi_header(u32 msg_hdr, struct scmi_msg_hdr *hdr)
 {
 	hdr->id = MSG_XTRACT_ID(msg_hdr);
 	hdr->protocol_id = MSG_XTRACT_PROT_ID(msg_hdr);
+	hdr->type = MSG_XTRACT_TYPE(msg_hdr);
 }
 
 /**
@@ -134,6 +152,27 @@ struct scmi_msg {
  *	buffer for the rx path as we use for the tx path.
  * @done: command message transmit completion event
  * @async_done: pointer to delayed response message received event completion
+ * @pending: True for xfers added to @pending_xfers hashtable
+ * @node: An hlist_node reference used to store this xfer, alternatively, on
+ *	  the free list @free_xfers or in the @pending_xfers hashtable
+ * @users: A refcount to track the active users for this xfer.
+ *	   This is meant to protect against the possibility that, when a command
+ *	   transaction times out concurrently with the reception of a valid
+ *	   response message, the xfer could be finally put on the TX path, and
+ *	   so vanish, while on the RX path scmi_rx_callback() is still
+ *	   processing it: in such a case this refcounting will ensure that, even
+ *	   though the timed-out transaction will anyway cause the command
+ *	   request to be reported as failed by time-out, the underlying xfer
+ *	   cannot be discarded and possibly reused until the last one user on
+ *	   the RX path has released it.
+ * @busy: An atomic flag to ensure exclusive write access to this xfer
+ * @state: The current state of this transfer, with states transitions deemed
+ *	   valid being:
+ *	    - SCMI_XFER_SENT_OK -> SCMI_XFER_RESP_OK [ -> SCMI_XFER_DRESP_OK ]
+ *	    - SCMI_XFER_SENT_OK -> SCMI_XFER_DRESP_OK
+ *	      (Missing synchronous response is assumed OK and ignored)
+ * @lock: A spinlock to protect state and busy fields.
+ * @priv: A pointer for transport private usage.
  */
 struct scmi_xfer {
 	int transfer_id;
@@ -142,8 +181,36 @@ struct scmi_xfer {
 	struct scmi_msg rx;
 	struct completion done;
 	struct completion *async_done;
+	bool pending;
+	struct hlist_node node;
+	refcount_t users;
+#define SCMI_XFER_FREE		0
+#define SCMI_XFER_BUSY		1
+	atomic_t busy;
+#define SCMI_XFER_SENT_OK	0
+#define SCMI_XFER_RESP_OK	1
+#define SCMI_XFER_DRESP_OK	2
+	int state;
+	/* A lock to protect state and busy fields */
+	spinlock_t lock;
+	void *priv;
 };
 
+/*
+ * An helper macro to lookup an xfer from the @pending_xfers hashtable
+ * using the message sequence number token as a key.
+ */
+#define XFER_FIND(__ht, __k)					\
+({								\
+	typeof(__k) k_ = __k;					\
+	struct scmi_xfer *xfer_ = NULL;				\
+								\
+	hash_for_each_possible((__ht), xfer_, node, k_)		\
+		if (xfer_->hdr.seq == k_)			\
+			break;					\
+	xfer_;							\
+})
+
 struct scmi_xfer_ops;
 
 /**
@@ -283,9 +350,13 @@ struct scmi_chan_info {
 /**
  * struct scmi_transport_ops - Structure representing a SCMI transport ops
  *
+ * @link_supplier: Optional callback to add link to a supplier device
  * @chan_available: Callback to check if channel is available or not
  * @chan_setup: Callback to allocate and setup a channel
  * @chan_free: Callback to free a channel
+ * @get_max_msg: Optional callback to provide max_msg dynamically
+ *		 Returns the maximum number of messages for the channel type
+ *		 (tx or rx) that can be pending simultaneously in the system
  * @send_message: Callback to send a message
  * @mark_txdone: Callback to mark tx as done
  * @fetch_response: Callback to fetch response
@@ -294,10 +365,12 @@ struct scmi_chan_info {
  * @poll_done: Callback to poll transfer status
  */
 struct scmi_transport_ops {
+	int (*link_supplier)(struct device *dev);
 	bool (*chan_available)(struct device *dev, int idx);
 	int (*chan_setup)(struct scmi_chan_info *cinfo, struct device *dev,
 			  bool tx);
 	int (*chan_free)(int id, void *p, void *data);
+	unsigned int (*get_max_msg)(struct scmi_chan_info *base_cinfo);
 	int (*send_message)(struct scmi_chan_info *cinfo,
 			    struct scmi_xfer *xfer);
 	void (*mark_txdone)(struct scmi_chan_info *cinfo, int ret);
@@ -317,25 +390,39 @@ struct scmi_device *scmi_child_dev_find(struct device *parent,
 /**
  * struct scmi_desc - Description of SoC integration
  *
+ * @transport_init: An optional function that a transport can provide to
+ *		    initialize some transport-specific setup during SCMI core
+ *		    initialization, so ahead of SCMI core probing.
+ * @transport_exit: An optional function that a transport can provide to
+ *		    de-initialize some transport-specific setup during SCMI core
+ *		    de-initialization, so after SCMI core removal.
  * @ops: Pointer to the transport specific ops structure
  * @max_rx_timeout_ms: Timeout for communication with SoC (in Milliseconds)
- * @max_msg: Maximum number of messages that can be pending
- *	simultaneously in the system
+ * @max_msg: Maximum number of messages for a channel type (tx or rx) that can
+ *	be pending simultaneously in the system. May be overridden by the
+ *	get_max_msg op.
  * @max_msg_size: Maximum size of data per message that can be handled.
  */
 struct scmi_desc {
+	int (*transport_init)(void);
+	void (*transport_exit)(void);
 	const struct scmi_transport_ops *ops;
 	int max_rx_timeout_ms;
 	int max_msg;
 	int max_msg_size;
 };
 
+#ifdef CONFIG_ARM_SCMI_TRANSPORT_MAILBOX
 extern const struct scmi_desc scmi_mailbox_desc;
-#ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
+#endif
+#ifdef CONFIG_ARM_SCMI_TRANSPORT_SMC
 extern const struct scmi_desc scmi_smc_desc;
 #endif
+#ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO
+extern const struct scmi_desc scmi_virtio_desc;
+#endif
 
-void scmi_rx_callback(struct scmi_chan_info *cinfo, u32 msg_hdr);
+void scmi_rx_callback(struct scmi_chan_info *cinfo, u32 msg_hdr, void *priv);
 void scmi_free_channel(struct scmi_chan_info *cinfo, struct idr *idr, int id);
 
 /* shmem related declarations */
@@ -352,8 +439,22 @@ void shmem_clear_channel(struct scmi_shared_mem __iomem *shmem);
 bool shmem_poll_done(struct scmi_shared_mem __iomem *shmem,
 		     struct scmi_xfer *xfer);
 
+/* declarations for message passing transports */
+struct scmi_msg_payld;
+
+/* Maximum overhead of message w.r.t. struct scmi_desc.max_msg_size */
+#define SCMI_MSG_MAX_PROT_OVERHEAD (2 * sizeof(__le32))
+
+size_t msg_response_size(struct scmi_xfer *xfer);
+size_t msg_command_size(struct scmi_xfer *xfer);
+void msg_tx_prepare(struct scmi_msg_payld *msg, struct scmi_xfer *xfer);
+u32 msg_read_header(struct scmi_msg_payld *msg);
+void msg_fetch_response(struct scmi_msg_payld *msg, size_t len,
+			struct scmi_xfer *xfer);
+void msg_fetch_notification(struct scmi_msg_payld *msg, size_t len,
+			    size_t max_len, struct scmi_xfer *xfer);
+
 void scmi_notification_instance_data_set(const struct scmi_handle *handle,
 					 void *priv);
 void *scmi_notification_instance_data_get(const struct scmi_handle *handle);
-
 #endif /* _SCMI_COMMON_H */
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 9b2e8d42a992..b406b3f78f46 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -21,6 +21,7 @@
 #include <linux/io.h>
 #include <linux/kernel.h>
 #include <linux/ktime.h>
+#include <linux/hashtable.h>
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/of_address.h>
@@ -67,16 +68,23 @@ struct scmi_requested_dev {
 /**
  * struct scmi_xfers_info - Structure to manage transfer information
  *
- * @xfer_block: Preallocated Message array
  * @xfer_alloc_table: Bitmap table for allocated messages.
  *	Index of this bitmap table is also used for message
  *	sequence identifier.
  * @xfer_lock: Protection for message allocation
+ * @max_msg: Maximum number of messages that can be pending
+ * @free_xfers: A free list for available to use xfers. It is initialized with
+ *		a number of xfers equal to the maximum allowed in-flight
+ *		messages.
+ * @pending_xfers: An hashtable, indexed by msg_hdr.seq, used to keep all the
+ *		   currently in-flight messages.
  */
 struct scmi_xfers_info {
-	struct scmi_xfer *xfer_block;
 	unsigned long *xfer_alloc_table;
 	spinlock_t xfer_lock;
+	int max_msg;
+	struct hlist_head free_xfers;
+	DECLARE_HASHTABLE(pending_xfers, SCMI_PENDING_XFERS_HT_ORDER_SZ);
 };
 
 /**
@@ -172,19 +180,6 @@ static inline int scmi_to_linux_errno(int errno)
 	return -EIO;
 }
 
-/**
- * scmi_dump_header_dbg() - Helper to dump a message header.
- *
- * @dev: Device pointer corresponding to the SCMI entity
- * @hdr: pointer to header.
- */
-static inline void scmi_dump_header_dbg(struct device *dev,
-					struct scmi_msg_hdr *hdr)
-{
-	dev_dbg(dev, "Message ID: %x Sequence ID: %x Protocol: %x\n",
-		hdr->id, hdr->seq, hdr->protocol_id);
-}
-
 void scmi_notification_instance_data_set(const struct scmi_handle *handle,
 					 void *priv)
 {
@@ -205,45 +200,189 @@ void *scmi_notification_instance_data_get(const struct scmi_handle *handle)
 }
 
 /**
+ * scmi_xfer_token_set  - Reserve and set new token for the xfer at hand
+ *
+ * @minfo: Pointer to Tx/Rx Message management info based on channel type
+ * @xfer: The xfer to act upon
+ *
+ * Pick the next unused monotonically increasing token and set it into
+ * xfer->hdr.seq: picking a monotonically increasing value avoids immediate
+ * reuse of freshly completed or timed-out xfers, thus mitigating the risk
+ * of incorrect association of a late and expired xfer with a live in-flight
+ * transaction, both happening to re-use the same token identifier.
+ *
+ * Since platform is NOT required to answer our request in-order we should
+ * account for a few rare but possible scenarios:
+ *
+ *  - exactly 'next_token' may be NOT available so pick xfer_id >= next_token
+ *    using find_next_zero_bit() starting from candidate next_token bit
+ *
+ *  - all tokens ahead upto (MSG_TOKEN_ID_MASK - 1) are used in-flight but we
+ *    are plenty of free tokens at start, so try a second pass using
+ *    find_next_zero_bit() and starting from 0.
+ *
+ *  X = used in-flight
+ *
+ * Normal
+ * ------
+ *
+ *		|- xfer_id picked
+ *   -----------+----------------------------------------------------------
+ *   | | |X|X|X| | | | | | ... ... ... ... ... ... ... ... ... ... ...|X|X|
+ *   ----------------------------------------------------------------------
+ *		^
+ *		|- next_token
+ *
+ * Out-of-order pending at start
+ * -----------------------------
+ *
+ *	  |- xfer_id picked, last_token fixed
+ *   -----+----------------------------------------------------------------
+ *   |X|X| | | | |X|X| ... ... ... ... ... ... ... ... ... ... ... ...|X| |
+ *   ----------------------------------------------------------------------
+ *    ^
+ *    |- next_token
+ *
+ *
+ * Out-of-order pending at end
+ * ---------------------------
+ *
+ *	  |- xfer_id picked, last_token fixed
+ *   -----+----------------------------------------------------------------
+ *   |X|X| | | | |X|X| ... ... ... ... ... ... ... ... ... ... |X|X|X||X|X|
+ *   ----------------------------------------------------------------------
+ *								^
+ *								|- next_token
+ *
+ * Context: Assumes to be called with @xfer_lock already acquired.
+ *
+ * Return: 0 on Success or error
+ */
+static int scmi_xfer_token_set(struct scmi_xfers_info *minfo,
+			       struct scmi_xfer *xfer)
+{
+	unsigned long xfer_id, next_token;
+
+	/*
+	 * Pick a candidate monotonic token in range [0, MSG_TOKEN_MAX - 1]
+	 * using the pre-allocated transfer_id as a base.
+	 * Note that the global transfer_id is shared across all message types
+	 * so there could be holes in the allocated set of monotonic sequence
+	 * numbers, but that is going to limit the effectiveness of the
+	 * mitigation only in very rare limit conditions.
+	 */
+	next_token = (xfer->transfer_id & (MSG_TOKEN_MAX - 1));
+
+	/* Pick the next available xfer_id >= next_token */
+	xfer_id = find_next_zero_bit(minfo->xfer_alloc_table,
+				     MSG_TOKEN_MAX, next_token);
+	if (xfer_id == MSG_TOKEN_MAX) {
+		/*
+		 * After heavily out-of-order responses, there are no free
+		 * tokens ahead, but only at start of xfer_alloc_table so
+		 * try again from the beginning.
+		 */
+		xfer_id = find_next_zero_bit(minfo->xfer_alloc_table,
+					     MSG_TOKEN_MAX, 0);
+		/*
+		 * Something is wrong if we got here since there can be a
+		 * maximum number of (MSG_TOKEN_MAX - 1) in-flight messages
+		 * but we have not found any free token [0, MSG_TOKEN_MAX - 1].
+		 */
+		if (WARN_ON_ONCE(xfer_id == MSG_TOKEN_MAX))
+			return -ENOMEM;
+	}
+
+	/* Update +/- last_token accordingly if we skipped some hole */
+	if (xfer_id != next_token)
+		atomic_add((int)(xfer_id - next_token), &transfer_last_id);
+
+	/* Set in-flight */
+	set_bit(xfer_id, minfo->xfer_alloc_table);
+	xfer->hdr.seq = (u16)xfer_id;
+
+	return 0;
+}
+
+/**
+ * scmi_xfer_token_clear  - Release the token
+ *
+ * @minfo: Pointer to Tx/Rx Message management info based on channel type
+ * @xfer: The xfer to act upon
+ */
+static inline void scmi_xfer_token_clear(struct scmi_xfers_info *minfo,
+					 struct scmi_xfer *xfer)
+{
+	clear_bit(xfer->hdr.seq, minfo->xfer_alloc_table);
+}
+
+/**
  * scmi_xfer_get() - Allocate one message
  *
  * @handle: Pointer to SCMI entity handle
  * @minfo: Pointer to Tx/Rx Message management info based on channel type
+ * @set_pending: If true a monotonic token is picked and the xfer is added to
+ *		 the pending hash table.
  *
  * Helper function which is used by various message functions that are
  * exposed to clients of this driver for allocating a message traffic event.
  *
- * This function can sleep depending on pending requests already in the system
- * for the SCMI entity. Further, this also holds a spinlock to maintain
- * integrity of internal data structures.
+ * Picks an xfer from the free list @free_xfers (if any available) and, if
+ * required, sets a monotonically increasing token and stores the inflight xfer
+ * into the @pending_xfers hashtable for later retrieval.
+ *
+ * The successfully initialized xfer is refcounted.
+ *
+ * Context: Holds @xfer_lock while manipulating @xfer_alloc_table and
+ *	    @free_xfers.
  *
  * Return: 0 if all went fine, else corresponding error.
  */
 static struct scmi_xfer *scmi_xfer_get(const struct scmi_handle *handle,
-				       struct scmi_xfers_info *minfo)
+				       struct scmi_xfers_info *minfo,
+				       bool set_pending)
 {
-	u16 xfer_id;
+	int ret;
+	unsigned long flags;
 	struct scmi_xfer *xfer;
-	unsigned long flags, bit_pos;
-	struct scmi_info *info = handle_to_scmi_info(handle);
 
-	/* Keep the locked section as small as possible */
 	spin_lock_irqsave(&minfo->xfer_lock, flags);
-	bit_pos = find_first_zero_bit(minfo->xfer_alloc_table,
-				      info->desc->max_msg);
-	if (bit_pos == info->desc->max_msg) {
+	if (hlist_empty(&minfo->free_xfers)) {
 		spin_unlock_irqrestore(&minfo->xfer_lock, flags);
 		return ERR_PTR(-ENOMEM);
 	}
-	set_bit(bit_pos, minfo->xfer_alloc_table);
-	spin_unlock_irqrestore(&minfo->xfer_lock, flags);
 
-	xfer_id = bit_pos;
+	/* grab an xfer from the free_list */
+	xfer = hlist_entry(minfo->free_xfers.first, struct scmi_xfer, node);
+	hlist_del_init(&xfer->node);
 
-	xfer = &minfo->xfer_block[xfer_id];
-	xfer->hdr.seq = xfer_id;
+	/*
+	 * Allocate transfer_id early so that can be used also as base for
+	 * monotonic sequence number generation if needed.
+	 */
 	xfer->transfer_id = atomic_inc_return(&transfer_last_id);
 
+	if (set_pending) {
+		/* Pick and set monotonic token */
+		ret = scmi_xfer_token_set(minfo, xfer);
+		if (!ret) {
+			hash_add(minfo->pending_xfers, &xfer->node,
+				 xfer->hdr.seq);
+			xfer->pending = true;
+		} else {
+			dev_err(handle->dev,
+				"Failed to get monotonic token %d\n", ret);
+			hlist_add_head(&xfer->node, &minfo->free_xfers);
+			xfer = ERR_PTR(ret);
+		}
+	}
+
+	if (!IS_ERR(xfer)) {
+		refcount_set(&xfer->users, 1);
+		atomic_set(&xfer->busy, SCMI_XFER_FREE);
+	}
+	spin_unlock_irqrestore(&minfo->xfer_lock, flags);
+
 	return xfer;
 }
 
@@ -253,6 +392,9 @@ static struct scmi_xfer *scmi_xfer_get(const struct scmi_handle *handle,
  * @minfo: Pointer to Tx/Rx Message management info based on channel type
  * @xfer: message that was reserved by scmi_xfer_get
  *
+ * After refcount check, possibly release an xfer, clearing the token slot,
+ * removing xfer from @pending_xfers and putting it back into free_xfers.
+ *
  * This holds a spinlock to maintain integrity of internal data structures.
  */
 static void
@@ -260,17 +402,215 @@ __scmi_xfer_put(struct scmi_xfers_info *minfo, struct scmi_xfer *xfer)
 {
 	unsigned long flags;
 
+	spin_lock_irqsave(&minfo->xfer_lock, flags);
+	if (refcount_dec_and_test(&xfer->users)) {
+		if (xfer->pending) {
+			scmi_xfer_token_clear(minfo, xfer);
+			hash_del(&xfer->node);
+			xfer->pending = false;
+		}
+		hlist_add_head(&xfer->node, &minfo->free_xfers);
+	}
+	spin_unlock_irqrestore(&minfo->xfer_lock, flags);
+}
+
+/**
+ * scmi_xfer_lookup_unlocked  -  Helper to lookup an xfer_id
+ *
+ * @minfo: Pointer to Tx/Rx Message management info based on channel type
+ * @xfer_id: Token ID to lookup in @pending_xfers
+ *
+ * Refcounting is untouched.
+ *
+ * Context: Assumes to be called with @xfer_lock already acquired.
+ *
+ * Return: A valid xfer on Success or error otherwise
+ */
+static struct scmi_xfer *
+scmi_xfer_lookup_unlocked(struct scmi_xfers_info *minfo, u16 xfer_id)
+{
+	struct scmi_xfer *xfer = NULL;
+
+	if (test_bit(xfer_id, minfo->xfer_alloc_table))
+		xfer = XFER_FIND(minfo->pending_xfers, xfer_id);
+
+	return xfer ?: ERR_PTR(-EINVAL);
+}
+
+/**
+ * scmi_msg_response_validate  - Validate message type against state of related
+ * xfer
+ *
+ * @cinfo: A reference to the channel descriptor.
+ * @msg_type: Message type to check
+ * @xfer: A reference to the xfer to validate against @msg_type
+ *
+ * This function checks if @msg_type is congruent with the current state of
+ * a pending @xfer; if an asynchronous delayed response is received before the
+ * related synchronous response (Out-of-Order Delayed Response) the missing
+ * synchronous response is assumed to be OK and completed, carrying on with the
+ * Delayed Response: this is done to address the case in which the underlying
+ * SCMI transport can deliver such out-of-order responses.
+ *
+ * Context: Assumes to be called with xfer->lock already acquired.
+ *
+ * Return: 0 on Success, error otherwise
+ */
+static inline int scmi_msg_response_validate(struct scmi_chan_info *cinfo,
+					     u8 msg_type,
+					     struct scmi_xfer *xfer)
+{
 	/*
-	 * Keep the locked section as small as possible
-	 * NOTE: we might escape with smp_mb and no lock here..
-	 * but just be conservative and symmetric.
+	 * Even if a response was indeed expected on this slot at this point,
+	 * a buggy platform could wrongly reply feeding us an unexpected
+	 * delayed response we're not prepared to handle: bail-out safely
+	 * blaming firmware.
 	 */
+	if (msg_type == MSG_TYPE_DELAYED_RESP && !xfer->async_done) {
+		dev_err(cinfo->dev,
+			"Delayed Response for %d not expected! Buggy F/W ?\n",
+			xfer->hdr.seq);
+		return -EINVAL;
+	}
+
+	switch (xfer->state) {
+	case SCMI_XFER_SENT_OK:
+		if (msg_type == MSG_TYPE_DELAYED_RESP) {
+			/*
+			 * Delayed Response expected but delivered earlier.
+			 * Assume message RESPONSE was OK and skip state.
+			 */
+			xfer->hdr.status = SCMI_SUCCESS;
+			xfer->state = SCMI_XFER_RESP_OK;
+			complete(&xfer->done);
+			dev_warn(cinfo->dev,
+				 "Received valid OoO Delayed Response for %d\n",
+				 xfer->hdr.seq);
+		}
+		break;
+	case SCMI_XFER_RESP_OK:
+		if (msg_type != MSG_TYPE_DELAYED_RESP)
+			return -EINVAL;
+		break;
+	case SCMI_XFER_DRESP_OK:
+		/* No further message expected once in SCMI_XFER_DRESP_OK */
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * scmi_xfer_state_update  - Update xfer state
+ *
+ * @xfer: A reference to the xfer to update
+ * @msg_type: Type of message being processed.
+ *
+ * Note that this message is assumed to have been already successfully validated
+ * by @scmi_msg_response_validate(), so here we just update the state.
+ *
+ * Context: Assumes to be called on an xfer exclusively acquired using the
+ *	    busy flag.
+ */
+static inline void scmi_xfer_state_update(struct scmi_xfer *xfer, u8 msg_type)
+{
+	xfer->hdr.type = msg_type;
+
+	/* Unknown command types were already discarded earlier */
+	if (xfer->hdr.type == MSG_TYPE_COMMAND)
+		xfer->state = SCMI_XFER_RESP_OK;
+	else
+		xfer->state = SCMI_XFER_DRESP_OK;
+}
+
+static bool scmi_xfer_acquired(struct scmi_xfer *xfer)
+{
+	int ret;
+
+	ret = atomic_cmpxchg(&xfer->busy, SCMI_XFER_FREE, SCMI_XFER_BUSY);
+
+	return ret == SCMI_XFER_FREE;
+}
+
+/**
+ * scmi_xfer_command_acquire  -  Helper to lookup and acquire a command xfer
+ *
+ * @cinfo: A reference to the channel descriptor.
+ * @msg_hdr: A message header to use as lookup key
+ *
+ * When a valid xfer is found for the sequence number embedded in the provided
+ * msg_hdr, reference counting is properly updated and exclusive access to this
+ * xfer is granted till released with @scmi_xfer_command_release.
+ *
+ * Return: A valid @xfer on Success or error otherwise.
+ */
+static inline struct scmi_xfer *
+scmi_xfer_command_acquire(struct scmi_chan_info *cinfo, u32 msg_hdr)
+{
+	int ret;
+	unsigned long flags;
+	struct scmi_xfer *xfer;
+	struct scmi_info *info = handle_to_scmi_info(cinfo->handle);
+	struct scmi_xfers_info *minfo = &info->tx_minfo;
+	u8 msg_type = MSG_XTRACT_TYPE(msg_hdr);
+	u16 xfer_id = MSG_XTRACT_TOKEN(msg_hdr);
+
+	/* Are we even expecting this? */
 	spin_lock_irqsave(&minfo->xfer_lock, flags);
-	clear_bit(xfer->hdr.seq, minfo->xfer_alloc_table);
+	xfer = scmi_xfer_lookup_unlocked(minfo, xfer_id);
+	if (IS_ERR(xfer)) {
+		dev_err(cinfo->dev,
+			"Message for %d type %d is not expected!\n",
+			xfer_id, msg_type);
+		spin_unlock_irqrestore(&minfo->xfer_lock, flags);
+		return xfer;
+	}
+	refcount_inc(&xfer->users);
 	spin_unlock_irqrestore(&minfo->xfer_lock, flags);
+
+	spin_lock_irqsave(&xfer->lock, flags);
+	ret = scmi_msg_response_validate(cinfo, msg_type, xfer);
+	/*
+	 * If a pending xfer was found which was also in a congruent state with
+	 * the received message, acquire exclusive access to it setting the busy
+	 * flag.
+	 * Spins only on the rare limit condition of concurrent reception of
+	 * RESP and DRESP for the same xfer.
+	 */
+	if (!ret) {
+		spin_until_cond(scmi_xfer_acquired(xfer));
+		scmi_xfer_state_update(xfer, msg_type);
+	}
+	spin_unlock_irqrestore(&xfer->lock, flags);
+
+	if (ret) {
+		dev_err(cinfo->dev,
+			"Invalid message type:%d for %d - HDR:0x%X  state:%d\n",
+			msg_type, xfer_id, msg_hdr, xfer->state);
+		/* On error the refcount incremented above has to be dropped */
+		__scmi_xfer_put(minfo, xfer);
+		xfer = ERR_PTR(-EINVAL);
+	}
+
+	return xfer;
+}
+
+static inline void scmi_xfer_command_release(struct scmi_info *info,
+					     struct scmi_xfer *xfer)
+{
+	atomic_set(&xfer->busy, SCMI_XFER_FREE);
+	__scmi_xfer_put(&info->tx_minfo, xfer);
+}
+
+static inline void scmi_clear_channel(struct scmi_info *info,
+				      struct scmi_chan_info *cinfo)
+{
+	if (info->desc->ops->clear_channel)
+		info->desc->ops->clear_channel(cinfo);
 }
 
-static void scmi_handle_notification(struct scmi_chan_info *cinfo, u32 msg_hdr)
+static void scmi_handle_notification(struct scmi_chan_info *cinfo,
+				     u32 msg_hdr, void *priv)
 {
 	struct scmi_xfer *xfer;
 	struct device *dev = cinfo->dev;
@@ -279,16 +619,17 @@ static void scmi_handle_notification(struct scmi_chan_info *cinfo, u32 msg_hdr)
 	ktime_t ts;
 
 	ts = ktime_get_boottime();
-	xfer = scmi_xfer_get(cinfo->handle, minfo);
+	xfer = scmi_xfer_get(cinfo->handle, minfo, false);
 	if (IS_ERR(xfer)) {
 		dev_err(dev, "failed to get free message slot (%ld)\n",
 			PTR_ERR(xfer));
-		info->desc->ops->clear_channel(cinfo);
+		scmi_clear_channel(info, cinfo);
 		return;
 	}
 
 	unpack_scmi_header(msg_hdr, &xfer->hdr);
-	scmi_dump_header_dbg(dev, &xfer->hdr);
+	if (priv)
+		xfer->priv = priv;
 	info->desc->ops->fetch_notification(cinfo, info->desc->max_msg_size,
 					    xfer);
 	scmi_notify(cinfo->handle, xfer->hdr.protocol_id,
@@ -300,59 +641,41 @@ static void scmi_handle_notification(struct scmi_chan_info *cinfo, u32 msg_hdr)
 
 	__scmi_xfer_put(minfo, xfer);
 
-	info->desc->ops->clear_channel(cinfo);
+	scmi_clear_channel(info, cinfo);
 }
 
 static void scmi_handle_response(struct scmi_chan_info *cinfo,
-				 u16 xfer_id, u8 msg_type)
+				 u32 msg_hdr, void *priv)
 {
 	struct scmi_xfer *xfer;
-	struct device *dev = cinfo->dev;
 	struct scmi_info *info = handle_to_scmi_info(cinfo->handle);
-	struct scmi_xfers_info *minfo = &info->tx_minfo;
 
-	/* Are we even expecting this? */
-	if (!test_bit(xfer_id, minfo->xfer_alloc_table)) {
-		dev_err(dev, "message for %d is not expected!\n", xfer_id);
-		info->desc->ops->clear_channel(cinfo);
-		return;
-	}
-
-	xfer = &minfo->xfer_block[xfer_id];
-	/*
-	 * Even if a response was indeed expected on this slot at this point,
-	 * a buggy platform could wrongly reply feeding us an unexpected
-	 * delayed response we're not prepared to handle: bail-out safely
-	 * blaming firmware.
-	 */
-	if (unlikely(msg_type == MSG_TYPE_DELAYED_RESP && !xfer->async_done)) {
-		dev_err(dev,
-			"Delayed Response for %d not expected! Buggy F/W ?\n",
-			xfer_id);
-		info->desc->ops->clear_channel(cinfo);
-		/* It was unexpected, so nobody will clear the xfer if not us */
-		__scmi_xfer_put(minfo, xfer);
+	xfer = scmi_xfer_command_acquire(cinfo, msg_hdr);
+	if (IS_ERR(xfer)) {
+		scmi_clear_channel(info, cinfo);
 		return;
 	}
 
 	/* rx.len could be shrunk in the sync do_xfer, so reset to maxsz */
-	if (msg_type == MSG_TYPE_DELAYED_RESP)
+	if (xfer->hdr.type == MSG_TYPE_DELAYED_RESP)
 		xfer->rx.len = info->desc->max_msg_size;
 
-	scmi_dump_header_dbg(dev, &xfer->hdr);
-
+	if (priv)
+		xfer->priv = priv;
 	info->desc->ops->fetch_response(cinfo, xfer);
 
 	trace_scmi_rx_done(xfer->transfer_id, xfer->hdr.id,
 			   xfer->hdr.protocol_id, xfer->hdr.seq,
-			   msg_type);
+			   xfer->hdr.type);
 
-	if (msg_type == MSG_TYPE_DELAYED_RESP) {
-		info->desc->ops->clear_channel(cinfo);
+	if (xfer->hdr.type == MSG_TYPE_DELAYED_RESP) {
+		scmi_clear_channel(info, cinfo);
 		complete(xfer->async_done);
 	} else {
 		complete(&xfer->done);
 	}
+
+	scmi_xfer_command_release(info, xfer);
 }
 
 /**
@@ -360,6 +683,7 @@ static void scmi_handle_response(struct scmi_chan_info *cinfo,
  *
  * @cinfo: SCMI channel info
  * @msg_hdr: Message header
+ * @priv: Transport specific private data.
  *
  * Processes one received message to appropriate transfer information and
  * signals completion of the transfer.
@@ -367,18 +691,17 @@ static void scmi_handle_response(struct scmi_chan_info *cinfo,
  * NOTE: This function will be invoked in IRQ context, hence should be
  * as optimal as possible.
  */
-void scmi_rx_callback(struct scmi_chan_info *cinfo, u32 msg_hdr)
+void scmi_rx_callback(struct scmi_chan_info *cinfo, u32 msg_hdr, void *priv)
 {
-	u16 xfer_id = MSG_XTRACT_TOKEN(msg_hdr);
 	u8 msg_type = MSG_XTRACT_TYPE(msg_hdr);
 
 	switch (msg_type) {
 	case MSG_TYPE_NOTIFICATION:
-		scmi_handle_notification(cinfo, msg_hdr);
+		scmi_handle_notification(cinfo, msg_hdr, priv);
 		break;
 	case MSG_TYPE_COMMAND:
 	case MSG_TYPE_DELAYED_RESP:
-		scmi_handle_response(cinfo, xfer_id, msg_type);
+		scmi_handle_response(cinfo, msg_hdr, priv);
 		break;
 	default:
 		WARN_ONCE(1, "received unknown msg_type:%d\n", msg_type);
@@ -390,7 +713,7 @@ void scmi_rx_callback(struct scmi_chan_info *cinfo, u32 msg_hdr)
  * xfer_put() - Release a transmit message
  *
  * @ph: Pointer to SCMI protocol handle
- * @xfer: message that was reserved by scmi_xfer_get
+ * @xfer: message that was reserved by xfer_get_init
  */
 static void xfer_put(const struct scmi_protocol_handle *ph,
 		     struct scmi_xfer *xfer)
@@ -408,7 +731,12 @@ static bool scmi_xfer_done_no_timeout(struct scmi_chan_info *cinfo,
 {
 	struct scmi_info *info = handle_to_scmi_info(cinfo->handle);
 
+	/*
+	 * Poll also on xfer->done so that polling can be forcibly terminated
+	 * in case of out-of-order receptions of delayed responses
+	 */
 	return info->desc->ops->poll_done(cinfo, xfer) ||
+	       try_wait_for_completion(&xfer->done) ||
 	       ktime_after(ktime_get(), stop);
 }
 
@@ -432,6 +760,12 @@ static int do_xfer(const struct scmi_protocol_handle *ph,
 	struct device *dev = info->dev;
 	struct scmi_chan_info *cinfo;
 
+	if (xfer->hdr.poll_completion && !info->desc->ops->poll_done) {
+		dev_warn_once(dev,
+			      "Polling mode is not supported by transport.\n");
+		return -EINVAL;
+	}
+
 	/*
 	 * Initialise protocol id now from protocol handle to avoid it being
 	 * overridden by mistake (or malice) by the protocol code mangling with
@@ -448,6 +782,16 @@ static int do_xfer(const struct scmi_protocol_handle *ph,
 			      xfer->hdr.protocol_id, xfer->hdr.seq,
 			      xfer->hdr.poll_completion);
 
+	xfer->state = SCMI_XFER_SENT_OK;
+	/*
+	 * Even though spinlocking is not needed here since no race is possible
+	 * on xfer->state due to the monotonically increasing tokens allocation,
+	 * we must anyway ensure xfer->state initialization is not re-ordered
+	 * after the .send_message() to be sure that on the RX path an early
+	 * ISR calling scmi_rx_callback() cannot see an old stale xfer->state.
+	 */
+	smp_mb();
+
 	ret = info->desc->ops->send_message(cinfo, xfer);
 	if (ret < 0) {
 		dev_dbg(dev, "Failed to send message %d\n", ret);
@@ -458,11 +802,22 @@ static int do_xfer(const struct scmi_protocol_handle *ph,
 		ktime_t stop = ktime_add_ns(ktime_get(), SCMI_MAX_POLL_TO_NS);
 
 		spin_until_cond(scmi_xfer_done_no_timeout(cinfo, xfer, stop));
-
-		if (ktime_before(ktime_get(), stop))
-			info->desc->ops->fetch_response(cinfo, xfer);
-		else
+		if (ktime_before(ktime_get(), stop)) {
+			unsigned long flags;
+
+			/*
+			 * Do not fetch_response if an out-of-order delayed
+			 * response is being processed.
+			 */
+			spin_lock_irqsave(&xfer->lock, flags);
+			if (xfer->state == SCMI_XFER_SENT_OK) {
+				info->desc->ops->fetch_response(cinfo, xfer);
+				xfer->state = SCMI_XFER_RESP_OK;
+			}
+			spin_unlock_irqrestore(&xfer->lock, flags);
+		} else {
 			ret = -ETIMEDOUT;
+		}
 	} else {
 		/* And we wait for the response. */
 		timeout = msecs_to_jiffies(info->desc->max_rx_timeout_ms);
@@ -557,7 +912,7 @@ static int xfer_get_init(const struct scmi_protocol_handle *ph,
 	    tx_size > info->desc->max_msg_size)
 		return -ERANGE;
 
-	xfer = scmi_xfer_get(pi->handle, minfo);
+	xfer = scmi_xfer_get(pi->handle, minfo, true);
 	if (IS_ERR(xfer)) {
 		ret = PTR_ERR(xfer);
 		dev_err(dev, "failed to get free message slot(%d)\n", ret);
@@ -566,6 +921,7 @@ static int xfer_get_init(const struct scmi_protocol_handle *ph,
 
 	xfer->tx.len = tx_size;
 	xfer->rx.len = rx_size ? : info->desc->max_msg_size;
+	xfer->hdr.type = MSG_TYPE_COMMAND;
 	xfer->hdr.id = msg_id;
 	xfer->hdr.poll_completion = false;
 
@@ -1026,25 +1382,32 @@ static int __scmi_xfer_info_init(struct scmi_info *sinfo,
 	const struct scmi_desc *desc = sinfo->desc;
 
 	/* Pre-allocated messages, no more than what hdr.seq can support */
-	if (WARN_ON(!desc->max_msg || desc->max_msg > MSG_TOKEN_MAX)) {
+	if (WARN_ON(!info->max_msg || info->max_msg > MSG_TOKEN_MAX)) {
 		dev_err(dev,
 			"Invalid maximum messages %d, not in range [1 - %lu]\n",
-			desc->max_msg, MSG_TOKEN_MAX);
+			info->max_msg, MSG_TOKEN_MAX);
 		return -EINVAL;
 	}
 
-	info->xfer_block = devm_kcalloc(dev, desc->max_msg,
-					sizeof(*info->xfer_block), GFP_KERNEL);
-	if (!info->xfer_block)
-		return -ENOMEM;
+	hash_init(info->pending_xfers);
 
-	info->xfer_alloc_table = devm_kcalloc(dev, BITS_TO_LONGS(desc->max_msg),
+	/* Allocate a bitmask sized to hold MSG_TOKEN_MAX tokens */
+	info->xfer_alloc_table = devm_kcalloc(dev, BITS_TO_LONGS(MSG_TOKEN_MAX),
 					      sizeof(long), GFP_KERNEL);
 	if (!info->xfer_alloc_table)
 		return -ENOMEM;
 
-	/* Pre-initialize the buffer pointer to pre-allocated buffers */
-	for (i = 0, xfer = info->xfer_block; i < desc->max_msg; i++, xfer++) {
+	/*
+	 * Preallocate a number of xfers equal to max inflight messages,
+	 * pre-initialize the buffer pointer to pre-allocated buffers and
+	 * attach all of them to the free list
+	 */
+	INIT_HLIST_HEAD(&info->free_xfers);
+	for (i = 0; i < info->max_msg; i++) {
+		xfer = devm_kzalloc(dev, sizeof(*xfer), GFP_KERNEL);
+		if (!xfer)
+			return -ENOMEM;
+
 		xfer->rx.buf = devm_kcalloc(dev, sizeof(u8), desc->max_msg_size,
 					    GFP_KERNEL);
 		if (!xfer->rx.buf)
@@ -1052,6 +1415,10 @@ static int __scmi_xfer_info_init(struct scmi_info *sinfo,
 
 		xfer->tx.buf = xfer->rx.buf;
 		init_completion(&xfer->done);
+		spin_lock_init(&xfer->lock);
+
+		/* Add initialized xfer to the free list */
+		hlist_add_head(&xfer->node, &info->free_xfers);
 	}
 
 	spin_lock_init(&info->xfer_lock);
@@ -1059,10 +1426,40 @@ static int __scmi_xfer_info_init(struct scmi_info *sinfo,
 	return 0;
 }
 
+static int scmi_channels_max_msg_configure(struct scmi_info *sinfo)
+{
+	const struct scmi_desc *desc = sinfo->desc;
+
+	if (!desc->ops->get_max_msg) {
+		sinfo->tx_minfo.max_msg = desc->max_msg;
+		sinfo->rx_minfo.max_msg = desc->max_msg;
+	} else {
+		struct scmi_chan_info *base_cinfo;
+
+		base_cinfo = idr_find(&sinfo->tx_idr, SCMI_PROTOCOL_BASE);
+		if (!base_cinfo)
+			return -EINVAL;
+		sinfo->tx_minfo.max_msg = desc->ops->get_max_msg(base_cinfo);
+
+		/* RX channel is optional so can be skipped */
+		base_cinfo = idr_find(&sinfo->rx_idr, SCMI_PROTOCOL_BASE);
+		if (base_cinfo)
+			sinfo->rx_minfo.max_msg =
+				desc->ops->get_max_msg(base_cinfo);
+	}
+
+	return 0;
+}
+
 static int scmi_xfer_info_init(struct scmi_info *sinfo)
 {
-	int ret = __scmi_xfer_info_init(sinfo, &sinfo->tx_minfo);
+	int ret;
+
+	ret = scmi_channels_max_msg_configure(sinfo);
+	if (ret)
+		return ret;
 
+	ret = __scmi_xfer_info_init(sinfo, &sinfo->tx_minfo);
 	if (!ret && idr_find(&sinfo->rx_idr, SCMI_PROTOCOL_BASE))
 		ret = __scmi_xfer_info_init(sinfo, &sinfo->rx_minfo);
 
@@ -1390,6 +1787,21 @@ void scmi_protocol_device_unrequest(const struct scmi_device_id *id_table)
 	mutex_unlock(&scmi_requested_devices_mtx);
 }
 
+static int scmi_cleanup_txrx_channels(struct scmi_info *info)
+{
+	int ret;
+	struct idr *idr = &info->tx_idr;
+
+	ret = idr_for_each(idr, info->desc->ops->chan_free, idr);
+	idr_destroy(&info->tx_idr);
+
+	idr = &info->rx_idr;
+	ret = idr_for_each(idr, info->desc->ops->chan_free, idr);
+	idr_destroy(&info->rx_idr);
+
+	return ret;
+}
+
 static int scmi_probe(struct platform_device *pdev)
 {
 	int ret;
@@ -1424,13 +1836,19 @@ static int scmi_probe(struct platform_device *pdev)
 	handle->devm_protocol_get = scmi_devm_protocol_get;
 	handle->devm_protocol_put = scmi_devm_protocol_put;
 
+	if (desc->ops->link_supplier) {
+		ret = desc->ops->link_supplier(dev);
+		if (ret)
+			return ret;
+	}
+
 	ret = scmi_txrx_setup(info, dev, SCMI_PROTOCOL_BASE);
 	if (ret)
 		return ret;
 
 	ret = scmi_xfer_info_init(info);
 	if (ret)
-		return ret;
+		goto clear_txrx_setup;
 
 	if (scmi_notification_init(handle))
 		dev_err(dev, "SCMI Notifications NOT available.\n");
@@ -1443,7 +1861,7 @@ static int scmi_probe(struct platform_device *pdev)
 	ret = scmi_protocol_acquire(handle, SCMI_PROTOCOL_BASE);
 	if (ret) {
 		dev_err(dev, "unable to communicate with SCMI\n");
-		return ret;
+		goto notification_exit;
 	}
 
 	mutex_lock(&scmi_list_mutex);
@@ -1482,6 +1900,12 @@ static int scmi_probe(struct platform_device *pdev)
 	}
 
 	return 0;
+
+notification_exit:
+	scmi_notification_exit(&info->handle);
+clear_txrx_setup:
+	scmi_cleanup_txrx_channels(info);
+	return ret;
 }
 
 void scmi_free_channel(struct scmi_chan_info *cinfo, struct idr *idr, int id)
@@ -1493,7 +1917,6 @@ static int scmi_remove(struct platform_device *pdev)
 {
 	int ret = 0, id;
 	struct scmi_info *info = platform_get_drvdata(pdev);
-	struct idr *idr = &info->tx_idr;
 	struct device_node *child;
 
 	mutex_lock(&scmi_list_mutex);
@@ -1517,14 +1940,7 @@ static int scmi_remove(struct platform_device *pdev)
 	idr_destroy(&info->active_protocols);
 
 	/* Safe to free channels since no more users */
-	ret = idr_for_each(idr, info->desc->ops->chan_free, idr);
-	idr_destroy(&info->tx_idr);
-
-	idr = &info->rx_idr;
-	ret = idr_for_each(idr, info->desc->ops->chan_free, idr);
-	idr_destroy(&info->rx_idr);
-
-	return ret;
+	return scmi_cleanup_txrx_channels(info);
 }
 
 static ssize_t protocol_version_show(struct device *dev,
@@ -1575,12 +1991,15 @@ ATTRIBUTE_GROUPS(versions);
 
 /* Each compatible listed below must have descriptor associated with it */
 static const struct of_device_id scmi_of_match[] = {
-#ifdef CONFIG_MAILBOX
+#ifdef CONFIG_ARM_SCMI_TRANSPORT_MAILBOX
 	{ .compatible = "arm,scmi", .data = &scmi_mailbox_desc },
 #endif
-#ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
+#ifdef CONFIG_ARM_SCMI_TRANSPORT_SMC
 	{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
 #endif
+#ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO
+	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
+#endif
 	{ /* Sentinel */ },
 };
 
@@ -1596,10 +2015,69 @@ static struct platform_driver scmi_driver = {
 	.remove = scmi_remove,
 };
 
+/**
+ * __scmi_transports_setup  - Common helper to call transport-specific
+ * .init/.exit code if provided.
+ *
+ * @init: A flag to distinguish between init and exit.
+ *
+ * Note that, if provided, we invoke .init/.exit functions for all the
+ * transports currently compiled in.
+ *
+ * Return: 0 on Success.
+ */
+static inline int __scmi_transports_setup(bool init)
+{
+	int ret = 0;
+	const struct of_device_id *trans;
+
+	for (trans = scmi_of_match; trans->data; trans++) {
+		const struct scmi_desc *tdesc = trans->data;
+
+		if ((init && !tdesc->transport_init) ||
+		    (!init && !tdesc->transport_exit))
+			continue;
+
+		if (init)
+			ret = tdesc->transport_init();
+		else
+			tdesc->transport_exit();
+
+		if (ret) {
+			pr_err("SCMI transport %s FAILED initialization!\n",
+			       trans->compatible);
+			break;
+		}
+	}
+
+	return ret;
+}
+
+static int __init scmi_transports_init(void)
+{
+	return __scmi_transports_setup(true);
+}
+
+static void __exit scmi_transports_exit(void)
+{
+	__scmi_transports_setup(false);
+}
+
 static int __init scmi_driver_init(void)
 {
+	int ret;
+
+	/* Bail out if no SCMI transport was configured */
+	if (WARN_ON(!IS_ENABLED(CONFIG_ARM_SCMI_HAVE_TRANSPORT)))
+		return -EINVAL;
+
 	scmi_bus_init();
 
+	/* Initialize any compiled-in transport which provided an init/exit */
+	ret = scmi_transports_init();
+	if (ret)
+		return ret;
+
 	scmi_base_register();
 
 	scmi_clock_register();
@@ -1628,6 +2106,8 @@ static void __exit scmi_driver_exit(void)
 
 	scmi_bus_exit();
 
+	scmi_transports_exit();
+
 	platform_driver_unregister(&scmi_driver);
 }
 module_exit(scmi_driver_exit);
diff --git a/drivers/firmware/arm_scmi/mailbox.c b/drivers/firmware/arm_scmi/mailbox.c
index e3dcb58314ae..e09eb12bf421 100644
--- a/drivers/firmware/arm_scmi/mailbox.c
+++ b/drivers/firmware/arm_scmi/mailbox.c
@@ -43,7 +43,7 @@ static void rx_callback(struct mbox_client *cl, void *m)
 {
 	struct scmi_mailbox *smbox = client_to_scmi_mailbox(cl);
 
-	scmi_rx_callback(smbox->cinfo, shmem_read_header(smbox->shmem));
+	scmi_rx_callback(smbox->cinfo, shmem_read_header(smbox->shmem), NULL);
 }
 
 static bool mailbox_chan_available(struct device *dev, int idx)
diff --git a/drivers/firmware/arm_scmi/msg.c b/drivers/firmware/arm_scmi/msg.c
new file mode 100644
index 000000000000..d33a704e5814
--- /dev/null
+++ b/drivers/firmware/arm_scmi/msg.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * For transports using message passing.
+ *
+ * Derived from shm.c.
+ *
+ * Copyright (C) 2019-2021 ARM Ltd.
+ * Copyright (C) 2020-2021 OpenSynergy GmbH
+ */
+
+#include <linux/types.h>
+
+#include "common.h"
+
+/*
+ * struct scmi_msg_payld - Transport SDU layout
+ *
+ * The SCMI specification requires all parameters, message headers, return
+ * arguments or any protocol data to be expressed in little endian format only.
+ */
+struct scmi_msg_payld {
+	__le32 msg_header;
+	__le32 msg_payload[];
+};
+
+/**
+ * msg_command_size() - Actual size of transport SDU for command.
+ *
+ * @xfer: message which core has prepared for sending
+ *
+ * Return: transport SDU size.
+ */
+size_t msg_command_size(struct scmi_xfer *xfer)
+{
+	return sizeof(struct scmi_msg_payld) + xfer->tx.len;
+}
+
+/**
+ * msg_response_size() - Maximum size of transport SDU for response.
+ *
+ * @xfer: message which core has prepared for sending
+ *
+ * Return: transport SDU size.
+ */
+size_t msg_response_size(struct scmi_xfer *xfer)
+{
+	return sizeof(struct scmi_msg_payld) + sizeof(__le32) + xfer->rx.len;
+}
+
+/**
+ * msg_tx_prepare() - Set up transport SDU for command.
+ *
+ * @msg: transport SDU for command
+ * @xfer: message which is being sent
+ */
+void msg_tx_prepare(struct scmi_msg_payld *msg, struct scmi_xfer *xfer)
+{
+	msg->msg_header = cpu_to_le32(pack_scmi_header(&xfer->hdr));
+	if (xfer->tx.buf)
+		memcpy(msg->msg_payload, xfer->tx.buf, xfer->tx.len);
+}
+
+/**
+ * msg_read_header() - Read SCMI header from transport SDU.
+ *
+ * @msg: transport SDU
+ *
+ * Return: SCMI header
+ */
+u32 msg_read_header(struct scmi_msg_payld *msg)
+{
+	return le32_to_cpu(msg->msg_header);
+}
+
+/**
+ * msg_fetch_response() - Fetch response SCMI payload from transport SDU.
+ *
+ * @msg: transport SDU with response
+ * @len: transport SDU size
+ * @xfer: message being responded to
+ */
+void msg_fetch_response(struct scmi_msg_payld *msg, size_t len,
+			struct scmi_xfer *xfer)
+{
+	size_t prefix_len = sizeof(*msg) + sizeof(msg->msg_payload[0]);
+
+	xfer->hdr.status = le32_to_cpu(msg->msg_payload[0]);
+	xfer->rx.len = min_t(size_t, xfer->rx.len,
+			     len >= prefix_len ? len - prefix_len : 0);
+
+	/* Take a copy to the rx buffer.. */
+	memcpy(xfer->rx.buf, &msg->msg_payload[1], xfer->rx.len);
+}
+
+/**
+ * msg_fetch_notification() - Fetch notification payload from transport SDU.
+ *
+ * @msg: transport SDU with notification
+ * @len: transport SDU size
+ * @max_len: maximum SCMI payload size to fetch
+ * @xfer: notification message
+ */
+void msg_fetch_notification(struct scmi_msg_payld *msg, size_t len,
+			    size_t max_len, struct scmi_xfer *xfer)
+{
+	xfer->rx.len = min_t(size_t, max_len,
+			     len >= sizeof(*msg) ? len - sizeof(*msg) : 0);
+
+	/* Take a copy to the rx buffer.. */
+	memcpy(xfer->rx.buf, msg->msg_payload, xfer->rx.len);
+}
diff --git a/drivers/firmware/arm_scmi/smc.c b/drivers/firmware/arm_scmi/smc.c
index bed5596c7209..4effecc3bb46 100644
--- a/drivers/firmware/arm_scmi/smc.c
+++ b/drivers/firmware/arm_scmi/smc.c
@@ -154,7 +154,8 @@ static int smc_send_message(struct scmi_chan_info *cinfo,
 	if (scmi_info->irq)
 		wait_for_completion(&scmi_info->tx_complete);
 
-	scmi_rx_callback(scmi_info->cinfo, shmem_read_header(scmi_info->shmem));
+	scmi_rx_callback(scmi_info->cinfo,
+			 shmem_read_header(scmi_info->shmem), NULL);
 
 	mutex_unlock(&scmi_info->shmem_lock);
 
diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
new file mode 100644
index 000000000000..224577f86928
--- /dev/null
+++ b/drivers/firmware/arm_scmi/virtio.c
@@ -0,0 +1,491 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Virtio Transport driver for Arm System Control and Management Interface
+ * (SCMI).
+ *
+ * Copyright (C) 2020-2021 OpenSynergy.
+ * Copyright (C) 2021 ARM Ltd.
+ */
+
+/**
+ * DOC: Theory of Operation
+ *
+ * The scmi-virtio transport implements a driver for the virtio SCMI device.
+ *
+ * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
+ * channel (virtio eventq, P2A channel). Each channel is implemented through a
+ * virtqueue. Access to each virtqueue is protected by spinlocks.
+ */
+
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+
+#include <uapi/linux/virtio_ids.h>
+#include <uapi/linux/virtio_scmi.h>
+
+#include "common.h"
+
+#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
+#define VIRTIO_SCMI_MAX_PDU_SIZE \
+	(VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
+#define DESCRIPTORS_PER_TX_MSG 2
+
+/**
+ * struct scmi_vio_channel - Transport channel information
+ *
+ * @vqueue: Associated virtqueue
+ * @cinfo: SCMI Tx or Rx channel
+ * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
+ * @is_rx: Whether channel is an Rx channel
+ * @ready: Whether transport user is ready to hear about channel
+ * @max_msg: Maximum number of pending messages for this channel.
+ * @lock: Protects access to all members except ready.
+ * @ready_lock: Protects access to ready. If required, it must be taken before
+ *              lock.
+ */
+struct scmi_vio_channel {
+	struct virtqueue *vqueue;
+	struct scmi_chan_info *cinfo;
+	struct list_head free_list;
+	bool is_rx;
+	bool ready;
+	unsigned int max_msg;
+	/* lock to protect access to all members except ready. */
+	spinlock_t lock;
+	/* lock to rotects access to ready flag. */
+	spinlock_t ready_lock;
+};
+
+/**
+ * struct scmi_vio_msg - Transport PDU information
+ *
+ * @request: SDU used for commands
+ * @input: SDU used for (delayed) responses and notifications
+ * @list: List which scmi_vio_msg may be part of
+ * @rx_len: Input SDU size in bytes, once input has been received
+ */
+struct scmi_vio_msg {
+	struct scmi_msg_payld *request;
+	struct scmi_msg_payld *input;
+	struct list_head list;
+	unsigned int rx_len;
+};
+
+/* Only one SCMI VirtIO device can possibly exist */
+static struct virtio_device *scmi_vdev;
+
+static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
+{
+	return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
+}
+
+static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
+			       struct scmi_vio_msg *msg)
+{
+	struct scatterlist sg_in;
+	int rc;
+	unsigned long flags;
+
+	sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
+
+	spin_lock_irqsave(&vioch->lock, flags);
+
+	rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
+	if (rc)
+		dev_err_once(vioch->cinfo->dev,
+			     "failed to add to virtqueue (%d)\n", rc);
+	else
+		virtqueue_kick(vioch->vqueue);
+
+	spin_unlock_irqrestore(&vioch->lock, flags);
+
+	return rc;
+}
+
+static void scmi_finalize_message(struct scmi_vio_channel *vioch,
+				  struct scmi_vio_msg *msg)
+{
+	if (vioch->is_rx) {
+		scmi_vio_feed_vq_rx(vioch, msg);
+	} else {
+		unsigned long flags;
+
+		spin_lock_irqsave(&vioch->lock, flags);
+		list_add(&msg->list, &vioch->free_list);
+		spin_unlock_irqrestore(&vioch->lock, flags);
+	}
+}
+
+static void scmi_vio_complete_cb(struct virtqueue *vqueue)
+{
+	unsigned long ready_flags;
+	unsigned long flags;
+	unsigned int length;
+	struct scmi_vio_channel *vioch;
+	struct scmi_vio_msg *msg;
+	bool cb_enabled = true;
+
+	if (WARN_ON_ONCE(!vqueue->vdev->priv))
+		return;
+	vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
+
+	for (;;) {
+		spin_lock_irqsave(&vioch->ready_lock, ready_flags);
+
+		if (!vioch->ready) {
+			if (!cb_enabled)
+				(void)virtqueue_enable_cb(vqueue);
+			goto unlock_ready_out;
+		}
+
+		spin_lock_irqsave(&vioch->lock, flags);
+		if (cb_enabled) {
+			virtqueue_disable_cb(vqueue);
+			cb_enabled = false;
+		}
+		msg = virtqueue_get_buf(vqueue, &length);
+		if (!msg) {
+			if (virtqueue_enable_cb(vqueue))
+				goto unlock_out;
+			cb_enabled = true;
+		}
+		spin_unlock_irqrestore(&vioch->lock, flags);
+
+		if (msg) {
+			msg->rx_len = length;
+			scmi_rx_callback(vioch->cinfo,
+					 msg_read_header(msg->input), msg);
+
+			scmi_finalize_message(vioch, msg);
+		}
+
+		spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
+	}
+
+unlock_out:
+	spin_unlock_irqrestore(&vioch->lock, flags);
+unlock_ready_out:
+	spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
+}
+
+static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
+
+static vq_callback_t *scmi_vio_complete_callbacks[] = {
+	scmi_vio_complete_cb,
+	scmi_vio_complete_cb
+};
+
+static unsigned int virtio_get_max_msg(struct scmi_chan_info *base_cinfo)
+{
+	struct scmi_vio_channel *vioch = base_cinfo->transport_info;
+
+	return vioch->max_msg;
+}
+
+static int virtio_link_supplier(struct device *dev)
+{
+	if (!scmi_vdev) {
+		dev_notice_once(dev,
+				"Deferring probe after not finding a bound scmi-virtio device\n");
+		return -EPROBE_DEFER;
+	}
+
+	if (!device_link_add(dev, &scmi_vdev->dev,
+			     DL_FLAG_AUTOREMOVE_CONSUMER)) {
+		dev_err(dev, "Adding link to supplier virtio device failed\n");
+		return -ECANCELED;
+	}
+
+	return 0;
+}
+
+static bool virtio_chan_available(struct device *dev, int idx)
+{
+	struct scmi_vio_channel *channels, *vioch = NULL;
+
+	if (WARN_ON_ONCE(!scmi_vdev))
+		return false;
+
+	channels = (struct scmi_vio_channel *)scmi_vdev->priv;
+
+	switch (idx) {
+	case VIRTIO_SCMI_VQ_TX:
+		vioch = &channels[VIRTIO_SCMI_VQ_TX];
+		break;
+	case VIRTIO_SCMI_VQ_RX:
+		if (scmi_vio_have_vq_rx(scmi_vdev))
+			vioch = &channels[VIRTIO_SCMI_VQ_RX];
+		break;
+	default:
+		return false;
+	}
+
+	return vioch && !vioch->cinfo;
+}
+
+static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
+			     bool tx)
+{
+	unsigned long flags;
+	struct scmi_vio_channel *vioch;
+	int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
+	int i;
+
+	if (!scmi_vdev)
+		return -EPROBE_DEFER;
+
+	vioch = &((struct scmi_vio_channel *)scmi_vdev->priv)[index];
+
+	for (i = 0; i < vioch->max_msg; i++) {
+		struct scmi_vio_msg *msg;
+
+		msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
+		if (!msg)
+			return -ENOMEM;
+
+		if (tx) {
+			msg->request = devm_kzalloc(cinfo->dev,
+						    VIRTIO_SCMI_MAX_PDU_SIZE,
+						    GFP_KERNEL);
+			if (!msg->request)
+				return -ENOMEM;
+		}
+
+		msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
+					  GFP_KERNEL);
+		if (!msg->input)
+			return -ENOMEM;
+
+		if (tx) {
+			spin_lock_irqsave(&vioch->lock, flags);
+			list_add_tail(&msg->list, &vioch->free_list);
+			spin_unlock_irqrestore(&vioch->lock, flags);
+		} else {
+			scmi_vio_feed_vq_rx(vioch, msg);
+		}
+	}
+
+	spin_lock_irqsave(&vioch->lock, flags);
+	cinfo->transport_info = vioch;
+	/* Indirectly setting channel not available any more */
+	vioch->cinfo = cinfo;
+	spin_unlock_irqrestore(&vioch->lock, flags);
+
+	spin_lock_irqsave(&vioch->ready_lock, flags);
+	vioch->ready = true;
+	spin_unlock_irqrestore(&vioch->ready_lock, flags);
+
+	return 0;
+}
+
+static int virtio_chan_free(int id, void *p, void *data)
+{
+	unsigned long flags;
+	struct scmi_chan_info *cinfo = p;
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+
+	spin_lock_irqsave(&vioch->ready_lock, flags);
+	vioch->ready = false;
+	spin_unlock_irqrestore(&vioch->ready_lock, flags);
+
+	scmi_free_channel(cinfo, data, id);
+
+	spin_lock_irqsave(&vioch->lock, flags);
+	vioch->cinfo = NULL;
+	spin_unlock_irqrestore(&vioch->lock, flags);
+
+	return 0;
+}
+
+static int virtio_send_message(struct scmi_chan_info *cinfo,
+			       struct scmi_xfer *xfer)
+{
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+	struct scatterlist sg_out;
+	struct scatterlist sg_in;
+	struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
+	unsigned long flags;
+	int rc;
+	struct scmi_vio_msg *msg;
+
+	spin_lock_irqsave(&vioch->lock, flags);
+
+	if (list_empty(&vioch->free_list)) {
+		spin_unlock_irqrestore(&vioch->lock, flags);
+		return -EBUSY;
+	}
+
+	msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
+	list_del(&msg->list);
+
+	msg_tx_prepare(msg->request, xfer);
+
+	sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
+	sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
+
+	rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
+	if (rc) {
+		list_add(&msg->list, &vioch->free_list);
+		dev_err_once(vioch->cinfo->dev,
+			     "%s() failed to add to virtqueue (%d)\n", __func__,
+			     rc);
+	} else {
+		virtqueue_kick(vioch->vqueue);
+	}
+
+	spin_unlock_irqrestore(&vioch->lock, flags);
+
+	return rc;
+}
+
+static void virtio_fetch_response(struct scmi_chan_info *cinfo,
+				  struct scmi_xfer *xfer)
+{
+	struct scmi_vio_msg *msg = xfer->priv;
+
+	if (msg) {
+		msg_fetch_response(msg->input, msg->rx_len, xfer);
+		xfer->priv = NULL;
+	}
+}
+
+static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
+				      size_t max_len, struct scmi_xfer *xfer)
+{
+	struct scmi_vio_msg *msg = xfer->priv;
+
+	if (msg) {
+		msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
+		xfer->priv = NULL;
+	}
+}
+
+static const struct scmi_transport_ops scmi_virtio_ops = {
+	.link_supplier = virtio_link_supplier,
+	.chan_available = virtio_chan_available,
+	.chan_setup = virtio_chan_setup,
+	.chan_free = virtio_chan_free,
+	.get_max_msg = virtio_get_max_msg,
+	.send_message = virtio_send_message,
+	.fetch_response = virtio_fetch_response,
+	.fetch_notification = virtio_fetch_notification,
+};
+
+static int scmi_vio_probe(struct virtio_device *vdev)
+{
+	struct device *dev = &vdev->dev;
+	struct scmi_vio_channel *channels;
+	bool have_vq_rx;
+	int vq_cnt;
+	int i;
+	int ret;
+	struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
+
+	/* Only one SCMI VirtiO device allowed */
+	if (scmi_vdev)
+		return -EINVAL;
+
+	have_vq_rx = scmi_vio_have_vq_rx(vdev);
+	vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
+
+	channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
+	if (!channels)
+		return -ENOMEM;
+
+	if (have_vq_rx)
+		channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
+
+	ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
+			      scmi_vio_vqueue_names, NULL);
+	if (ret) {
+		dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
+		return ret;
+	}
+
+	for (i = 0; i < vq_cnt; i++) {
+		unsigned int sz;
+
+		spin_lock_init(&channels[i].lock);
+		spin_lock_init(&channels[i].ready_lock);
+		INIT_LIST_HEAD(&channels[i].free_list);
+		channels[i].vqueue = vqs[i];
+
+		sz = virtqueue_get_vring_size(channels[i].vqueue);
+		/* Tx messages need multiple descriptors. */
+		if (!channels[i].is_rx)
+			sz /= DESCRIPTORS_PER_TX_MSG;
+
+		if (sz > MSG_TOKEN_MAX) {
+			dev_info_once(dev,
+				      "%s virtqueue could hold %d messages. Only %ld allowed to be pending.\n",
+				      channels[i].is_rx ? "rx" : "tx",
+				      sz, MSG_TOKEN_MAX);
+			sz = MSG_TOKEN_MAX;
+		}
+		channels[i].max_msg = sz;
+	}
+
+	vdev->priv = channels;
+	scmi_vdev = vdev;
+
+	return 0;
+}
+
+static void scmi_vio_remove(struct virtio_device *vdev)
+{
+	vdev->config->reset(vdev);
+	vdev->config->del_vqs(vdev);
+	scmi_vdev = NULL;
+}
+
+static int scmi_vio_validate(struct virtio_device *vdev)
+{
+	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
+		dev_err(&vdev->dev,
+			"device does not comply with spec version 1.x\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static unsigned int features[] = {
+	VIRTIO_SCMI_F_P2A_CHANNELS,
+};
+
+static const struct virtio_device_id id_table[] = {
+	{ VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
+	{ 0 }
+};
+
+static struct virtio_driver virtio_scmi_driver = {
+	.driver.name = "scmi-virtio",
+	.driver.owner = THIS_MODULE,
+	.feature_table = features,
+	.feature_table_size = ARRAY_SIZE(features),
+	.id_table = id_table,
+	.probe = scmi_vio_probe,
+	.remove = scmi_vio_remove,
+	.validate = scmi_vio_validate,
+};
+
+static int __init virtio_scmi_init(void)
+{
+	return register_virtio_driver(&virtio_scmi_driver);
+}
+
+static void __exit virtio_scmi_exit(void)
+{
+	unregister_virtio_driver(&virtio_scmi_driver);
+}
+
+const struct scmi_desc scmi_virtio_desc = {
+	.transport_init = virtio_scmi_init,
+	.transport_exit = virtio_scmi_exit,
+	.ops = &scmi_virtio_ops,
+	.max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
+	.max_msg = 0, /* overridden by virtio_get_max_msg() */
+	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
+};
diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
index 47ea2bd42b10..ced1964faf42 100644
--- a/drivers/firmware/qcom_scm.c
+++ b/drivers/firmware/qcom_scm.c
@@ -71,7 +71,7 @@ static struct qcom_scm_wb_entry qcom_scm_wb[] = {
 	{ .flag = QCOM_SCM_FLAG_WARMBOOT_CPU3 },
 };
 
-static const char *qcom_scm_convention_names[] = {
+static const char * const qcom_scm_convention_names[] = {
 	[SMC_CONVENTION_UNKNOWN] = "unknown",
 	[SMC_CONVENTION_ARM_32] = "smc arm 32",
 	[SMC_CONVENTION_ARM_64] = "smc arm 64",
@@ -331,7 +331,7 @@ int qcom_scm_set_cold_boot_addr(void *entry, const cpumask_t *cpus)
 		.owner = ARM_SMCCC_OWNER_SIP,
 	};
 
-	if (!cpus || (cpus && cpumask_empty(cpus)))
+	if (!cpus || cpumask_empty(cpus))
 		return -EINVAL;
 
 	for_each_cpu(cpu, cpus) {
@@ -1299,6 +1299,7 @@ static const struct of_device_id qcom_scm_dt_match[] = {
 	{ .compatible = "qcom,scm" },
 	{}
 };
+MODULE_DEVICE_TABLE(of, qcom_scm_dt_match);
 
 static struct platform_driver qcom_scm_driver = {
 	.driver = {
@@ -1315,3 +1316,6 @@ static int __init qcom_scm_init(void)
 	return platform_driver_register(&qcom_scm_driver);
 }
 subsys_initcall(qcom_scm_init);
+
+MODULE_DESCRIPTION("Qualcomm Technologies, Inc. SCM driver");
+MODULE_LICENSE("GPL v2");
diff --git a/drivers/firmware/tegra/bpmp-debugfs.c b/drivers/firmware/tegra/bpmp-debugfs.c
index 440d99c63638..3e9fa4b54358 100644
--- a/drivers/firmware/tegra/bpmp-debugfs.c
+++ b/drivers/firmware/tegra/bpmp-debugfs.c
@@ -296,25 +296,61 @@ static int bpmp_debug_show(struct seq_file *m, void *p)
 	struct file *file = m->private;
 	struct inode *inode = file_inode(file);
 	struct tegra_bpmp *bpmp = inode->i_private;
-	char *databuf = NULL;
 	char fnamebuf[256];
 	const char *filename;
-	uint32_t nbytes = 0;
-	size_t len;
-	int err;
-
-	len = seq_get_buf(m, &databuf);
-	if (!databuf)
-		return -ENOMEM;
+	struct mrq_debug_request req = {
+		.cmd = cpu_to_le32(CMD_DEBUG_READ),
+	};
+	struct mrq_debug_response resp;
+	struct tegra_bpmp_message msg = {
+		.mrq = MRQ_DEBUG,
+		.tx = {
+			.data = &req,
+			.size = sizeof(req),
+		},
+		.rx = {
+			.data = &resp,
+			.size = sizeof(resp),
+		},
+	};
+	uint32_t fd = 0, len = 0;
+	int remaining, err;
 
 	filename = get_filename(bpmp, file, fnamebuf, sizeof(fnamebuf));
 	if (!filename)
 		return -ENOENT;
 
-	err = mrq_debug_read(bpmp, filename, databuf, len, &nbytes);
-	if (!err)
-		seq_commit(m, nbytes);
+	mutex_lock(&bpmp_debug_lock);
+	err = mrq_debug_open(bpmp, filename, &fd, &len, 0);
+	if (err)
+		goto out;
+
+	req.frd.fd = fd;
+	remaining = len;
+
+	while (remaining > 0) {
+		err = tegra_bpmp_transfer(bpmp, &msg);
+		if (err < 0) {
+			goto close;
+		} else if (msg.rx.ret < 0) {
+			err = -EINVAL;
+			goto close;
+		}
 
+		if (resp.frd.readlen > remaining) {
+			pr_err("%s: read data length invalid\n", __func__);
+			err = -EINVAL;
+			goto close;
+		}
+
+		seq_write(m, resp.frd.data, resp.frd.readlen);
+		remaining -= resp.frd.readlen;
+	}
+
+close:
+	err = mrq_debug_close(bpmp, fd);
+out:
+	mutex_unlock(&bpmp_debug_lock);
 	return err;
 }