PCI: Add pci_enable_atomic_ops_to_root()

The Atomic Operations feature (PCIe r4.0, sec 6.15) allows atomic
transctions to be requested by, routed through and completed by PCIe
components. Routing and completion do not require software support.
Component support for each is detectable via the DEVCAP2 register.

A Requester may use AtomicOps only if its PCI_EXP_DEVCTL2_ATOMIC_REQ is
set. This should be set only if the Completer and all intermediate routing
elements support AtomicOps.

A concrete example is the AMD Fiji-class GPU (which is capable of making
AtomicOp requests), below a PLX 8747 switch (advertising AtomicOp routing)
with a Haswell host bridge (advertising AtomicOp completion support).

Add pci_enable_atomic_ops_to_root() for per-device control over AtomicOp
requests. This checks to be sure the Root Port supports completion of the
desired AtomicOp sizes and the path to the Root Port supports routing the
AtomicOps.

Signed-off-by: Jay Cornwall <Jay.Cornwall@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
[bhelgaas: changelog, comments, whitespace]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 75 insertions, 0 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 4a7c6864fdf4..6112dd8d68b6 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3066,6 +3066,81 @@ int pci_rebar_set_size(struct pci_dev *pdev, int bar, int size)
 }
 
 /**
+ * pci_enable_atomic_ops_to_root - enable AtomicOp requests to root port
+ * @dev: the PCI device
+ * @cap_mask: mask of desired AtomicOp sizes, including one or more of:
+ *	PCI_EXP_DEVCAP2_ATOMIC_COMP32
+ *	PCI_EXP_DEVCAP2_ATOMIC_COMP64
+ *	PCI_EXP_DEVCAP2_ATOMIC_COMP128
+ *
+ * Return 0 if all upstream bridges support AtomicOp routing, egress
+ * blocking is disabled on all upstream ports, and the root port supports
+ * the requested completion capabilities (32-bit, 64-bit and/or 128-bit
+ * AtomicOp completion), or negative otherwise.
+ */
+int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask)
+{
+	struct pci_bus *bus = dev->bus;
+	struct pci_dev *bridge;
+	u32 cap, ctl2;
+
+	if (!pci_is_pcie(dev))
+		return -EINVAL;
+
+	/*
+	 * Per PCIe r4.0, sec 6.15, endpoints and root ports may be
+	 * AtomicOp requesters.  For now, we only support endpoints as
+	 * requesters and root ports as completers.  No endpoints as
+	 * completers, and no peer-to-peer.
+	 */
+
+	switch (pci_pcie_type(dev)) {
+	case PCI_EXP_TYPE_ENDPOINT:
+	case PCI_EXP_TYPE_LEG_END:
+	case PCI_EXP_TYPE_RC_END:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	while (bus->parent) {
+		bridge = bus->self;
+
+		pcie_capability_read_dword(bridge, PCI_EXP_DEVCAP2, &cap);
+
+		switch (pci_pcie_type(bridge)) {
+		/* Ensure switch ports support AtomicOp routing */
+		case PCI_EXP_TYPE_UPSTREAM:
+		case PCI_EXP_TYPE_DOWNSTREAM:
+			if (!(cap & PCI_EXP_DEVCAP2_ATOMIC_ROUTE))
+				return -EINVAL;
+			break;
+
+		/* Ensure root port supports all the sizes we care about */
+		case PCI_EXP_TYPE_ROOT_PORT:
+			if ((cap & cap_mask) != cap_mask)
+				return -EINVAL;
+			break;
+		}
+
+		/* Ensure upstream ports don't block AtomicOps on egress */
+		if (!bridge->has_secondary_link) {
+			pcie_capability_read_dword(bridge, PCI_EXP_DEVCTL2,
+						   &ctl2);
+			if (ctl2 & PCI_EXP_DEVCTL2_ATOMIC_EGRESS_BLOCK)
+				return -EINVAL;
+		}
+
+		bus = bus->parent;
+	}
+
+	pcie_capability_set_word(dev, PCI_EXP_DEVCTL2,
+				 PCI_EXP_DEVCTL2_ATOMIC_REQ);
+	return 0;
+}
+EXPORT_SYMBOL(pci_enable_atomic_ops_to_root);
+
+/**
  * pci_swizzle_interrupt_pin - swizzle INTx for device behind bridge
  * @dev: the PCI device
  * @pin: the INTx pin (1=INTA, 2=INTB, 3=INTC, 4=INTD)