platform/chrome: wilco_ec: Standardize mailbox interface

The current API for the wilco EC mailbox interface is bad.

It assumes that most messages sent to the EC follow a similar structure,
with a command byte in MBOX[0], followed by a junk byte, followed by
actual data. This doesn't happen in several cases, such as setting the
RTC time, using the raw debugfs interface, and reading or writing
properties such as the Peak Shift policy (this last to be submitted soon).

Similarly for the response message from the EC, the current interface
assumes that the first byte of data is always 0, and the second byte
is unused. However, in both setting and getting the RTC time, in the
debugfs interface, and for reading and writing properties, this isn't
true.

The current way to resolve this is to use WILCO_EC_FLAG_RAW* flags to
specify when and when not to skip these initial bytes in the sent and
received message. They are confusing and used so much that they are
normal, and not exceptions. In addition, the first byte of
response in the debugfs interface is still always skipped, which is
weird, since this raw interface should be giving the entire result.

Additionally, sent messages assume the first byte is a command, and so
struct wilco_ec_message contains the "command" field. In setting or
getting properties however, the first byte is not a command, and so this
field has to be filled with a byte that isn't actually a command. This
is again inconsistent.

wilco_ec_message contains a result field as well, copied from
wilco_ec_response->result. The message result field should be removed:
if the message fails, the cause is already logged, and the callers are
alerted. They will never care about the actual state of the result flag.

These flags and different cases make the wilco_ec_transfer() function,
used in wilco_ec_mailbox(), really gross, dealing with a bunch of
different cases. It's difficult to figure out what it is doing.

Finally, making these assumptions about the structure of a message make
it so that the messages do not correspond well with the specification
for the EC's mailbox interface. For instance, this interface
specification may say that MBOX[9] in the received message contains
some information, but the calling code needs to remember that the first
byte of response is always skipped, and because it didn't set the
RESPONSE_RAW flag, the next byte is also skipped, so this information
is actually contained within wilco_ec_message->response_data[7]. This
makes it difficult to maintain this code in the future.

To fix these problems this patch standardizes the mailbox interface by:
- Removing the WILCO_EC_FLAG_RAW* flags
- Removing the command and reserved_raw bytes from wilco_ec_request
- Removing the mbox0 byte from wilco_ec_response
- Simplifying wilco_ec_transfer() because of these changes
- Gives the callers of wilco_ec_mailbox() the responsibility of exactly
  and consistently defining the structure of the mailbox request and
  response
- Removing command and result from wilco_ec_message.

This results in the reduction of total code, and makes it much more
maintainable and understandable.

Signed-off-by: Nick Crews <ncrews@chromium.org>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

2 files changed, 29 insertions, 66 deletions

diff --git a/drivers/platform/chrome/wilco_ec/debugfs.c b/drivers/platform/chrome/wilco_ec/debugfs.c
index c090db2cd5be..8d307378c1cb 100644
--- a/drivers/platform/chrome/wilco_ec/debugfs.c
+++ b/drivers/platform/chrome/wilco_ec/debugfs.c
@@ -4,31 +4,7 @@
  *
  * Copyright 2019 Google LLC
  *
- * There is only one attribute used for debugging, called raw.
- * You can write a hexadecimal sentence to raw, and that series of bytes
- * will be sent to the EC. Then, you can read the bytes of response
- * by reading from raw.
- *
- * For writing:
- * Bytes 0-1 indicate the message type:
- *         00 F0 = Execute Legacy Command
- *         00 F2 = Read/Write NVRAM Property
- * Byte 2 provides the command code
- * Bytes 3+ consist of the data passed in the request
- *
- * When referencing the EC interface spec, byte 2 corresponds to MBOX[0],
- * byte 3 corresponds to MBOX[1], etc.
- *
- * At least three bytes are required, for the msg type and command,
- * with additional bytes optional for additional data.
- *
- * Example:
- * // Request EC info type 3 (EC firmware build date)
- * $ echo 00 f0 38 00 03 00 > raw
- * // View the result. The decoded ASCII result "12/21/18" is
- * // included after the raw hex.
- * $ cat raw
- * 00 31 32 2f 32 31 2f 31 38 00 38 00 01 00 2f 00  .12/21/18.8...
+ * See Documentation/ABI/testing/debugfs-wilco-ec for usage.
  */
 
 #include <linux/ctype.h>
@@ -136,18 +112,15 @@ static ssize_t raw_write(struct file *file, const char __user *user_buf,
 	ret = parse_hex_sentence(buf, kcount, request_data, TYPE_AND_DATA_SIZE);
 	if (ret < 0)
 		return ret;
-	/* Need at least two bytes for message type and one for command */
+	/* Need at least two bytes for message type and one byte of data */
 	if (ret < 3)
 		return -EINVAL;
 
-	/* Clear response data buffer */
-	memset(debug_info->raw_data, '\0', EC_MAILBOX_DATA_SIZE_EXTENDED);
-
 	msg.type = request_data[0] << 8 | request_data[1];
-	msg.flags = WILCO_EC_FLAG_RAW;
-	msg.command = request_data[2];
-	msg.request_data = ret > 3 ? request_data + 3 : 0;
-	msg.request_size = ret - 3;
+	msg.flags = 0;
+	msg.request_data = request_data + 2;
+	msg.request_size = ret - 2;
+	memset(debug_info->raw_data, 0, sizeof(debug_info->raw_data));
 	msg.response_data = debug_info->raw_data;
 	msg.response_size = EC_MAILBOX_DATA_SIZE;
 
@@ -174,7 +147,8 @@ static ssize_t raw_read(struct file *file, char __user *user_buf, size_t count,
 		fmt_len = hex_dump_to_buffer(debug_info->raw_data,
 					     debug_info->response_size,
 					     16, 1, debug_info->formatted_data,
-					     FORMATTED_BUFFER_SIZE, true);
+					     sizeof(debug_info->formatted_data),
+					     true);
 		/* Only return response the first time it is read */
 		debug_info->response_size = 0;
 	}
diff --git a/drivers/platform/chrome/wilco_ec/mailbox.c b/drivers/platform/chrome/wilco_ec/mailbox.c
index 14355668ddfa..7fb58b487963 100644
--- a/drivers/platform/chrome/wilco_ec/mailbox.c
+++ b/drivers/platform/chrome/wilco_ec/mailbox.c
@@ -92,21 +92,10 @@ static void wilco_ec_prepare(struct wilco_ec_message *msg,
 			     struct wilco_ec_request *rq)
 {
 	memset(rq, 0, sizeof(*rq));
-
-	/* Handle messages without trimming bytes from the request */
-	if (msg->request_size && msg->flags & WILCO_EC_FLAG_RAW_REQUEST) {
-		rq->reserved_raw = *(u8 *)msg->request_data;
-		msg->request_size--;
-		memmove(msg->request_data, msg->request_data + 1,
-			msg->request_size);
-	}
-
-	/* Fill in request packet */
 	rq->struct_version = EC_MAILBOX_PROTO_VERSION;
 	rq->mailbox_id = msg->type;
 	rq->mailbox_version = EC_MAILBOX_VERSION;
-	rq->data_size = msg->request_size + EC_MAILBOX_DATA_EXTRA;
-	rq->command = msg->command;
+	rq->data_size = msg->request_size;
 
 	/* Checksum header and data */
 	rq->checksum = wilco_ec_checksum(rq, sizeof(*rq));
@@ -159,6 +148,12 @@ static int wilco_ec_transfer(struct wilco_ec_device *ec,
 		return -EIO;
 	}
 
+	/*
+	 * The EC always returns either EC_MAILBOX_DATA_SIZE or
+	 * EC_MAILBOX_DATA_SIZE_EXTENDED bytes of data, so we need to
+	 * calculate the checksum on **all** of this data, even if we
+	 * won't use all of it.
+	 */
 	if (msg->flags & WILCO_EC_FLAG_EXTENDED_DATA)
 		size = EC_MAILBOX_DATA_SIZE_EXTENDED;
 	else
@@ -173,33 +168,26 @@ static int wilco_ec_transfer(struct wilco_ec_device *ec,
 		return -EBADMSG;
 	}
 
-	/* Check that the EC reported success */
-	msg->result = rs->result;
-	if (msg->result) {
-		dev_dbg(ec->dev, "bad response: 0x%02x\n", msg->result);
+	if (rs->result) {
+		dev_dbg(ec->dev, "EC reported failure: 0x%02x\n", rs->result);
 		return -EBADMSG;
 	}
 
-	/* Check the returned data size, skipping the header */
 	if (rs->data_size != size) {
 		dev_dbg(ec->dev, "unexpected packet size (%u != %zu)",
 			rs->data_size, size);
 		return -EMSGSIZE;
 	}
 
-	/* Skip 1 response data byte unless specified */
-	size = (msg->flags & WILCO_EC_FLAG_RAW_RESPONSE) ? 0 : 1;
-	if ((ssize_t) rs->data_size - size < msg->response_size) {
-		dev_dbg(ec->dev, "response data too short (%zd < %zu)",
-			(ssize_t) rs->data_size - size, msg->response_size);
+	if (rs->data_size < msg->response_size) {
+		dev_dbg(ec->dev, "EC didn't return enough data (%u < %zu)",
+			rs->data_size, msg->response_size);
 		return -EMSGSIZE;
 	}
 
-	/* Ignore response data bytes as requested */
-	memcpy(msg->response_data, rs->data + size, msg->response_size);
+	memcpy(msg->response_data, rs->data, msg->response_size);
 
-	/* Return actual amount of data received */
-	return msg->response_size;
+	return rs->data_size;
 }
 
 /**
@@ -207,10 +195,12 @@ static int wilco_ec_transfer(struct wilco_ec_device *ec,
  * @ec: EC device.
  * @msg: EC message data for request and response.
  *
- * On entry msg->type, msg->flags, msg->command, msg->request_size,
- * msg->response_size, and msg->request_data should all be filled in.
+ * On entry msg->type, msg->request_size, and msg->request_data should all be
+ * filled in. If desired, msg->flags can be set.
  *
- * On exit msg->result and msg->response_data will be filled.
+ * If a response is expected, msg->response_size should be set, and
+ * msg->response_data should point to a buffer with enough space. On exit
+ * msg->response_data will be filled.
  *
  * Return: number of bytes received or negative error code on failure.
  */
@@ -219,9 +209,8 @@ int wilco_ec_mailbox(struct wilco_ec_device *ec, struct wilco_ec_message *msg)
 	struct wilco_ec_request *rq;
 	int ret;
 
-	dev_dbg(ec->dev, "cmd=%02x type=%04x flags=%02x rslen=%zu rqlen=%zu\n",
-		msg->command, msg->type, msg->flags, msg->response_size,
-		msg->request_size);
+	dev_dbg(ec->dev, "type=%04x flags=%02x rslen=%zu rqlen=%zu\n",
+		msg->type, msg->flags, msg->response_size, msg->request_size);
 
 	mutex_lock(&ec->mailbox_lock);
 	/* Prepare request packet */