linux-kernel - [PATCH] platform/chrome: cros_ec_proto: Lock device when updating MKBP version

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Message-ID: <20240725175714.1769080-1-patrykd@google.com>
Date: Thu, 25 Jul 2024 17:57:13 +0000
From: Patryk Duda <patrykd@...gle.com>
To: Guenter Roeck <groeck@...omium.org>, Tzung-Bi Shih <tzungbi@...nel.org>, 
	Benson Leung <bleung@...omium.org>
Cc: chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Patryk Duda <patrykd@...gle.com>
Subject: [PATCH] platform/chrome: cros_ec_proto: Lock device when updating
 MKBP version

The cros_ec_get_host_command_version_mask() function requires that the
caller must have ec_dev->lock mutex before calling it. This requirement
was not met and as a result it was possible that two commands were sent
to the device at the same time.

The problem was observed while using UART backend which doesn't use any
additional locks, unlike SPI backend which locks the controller until
response is received.

Fixes: f74c7557ed0d ("platform/chrome: cros_ec_proto: Update version on GET_NEXT_EVENT failure")
Cc: stable@...r.kernel.org
Signed-off-by: Patryk Duda <patrykd@...gle.com>
---
The f74c7557ed0d patch was tested with Fingerprint MCU (FPMCU) that uses
SPI to communicate with chipset. At that time, UART FPMCU had the same
version of GET_NEXT_EVENT command in RO and RW, so the MKBP version was
never updated in this case.

Version 3 of GET_NEXT_EVENT command was recently added to CrosEC. As a
result MKBP version is also updated when UART FPMCU is used which
exposed this problem.

Best regards,
Patryk

 drivers/platform/chrome/cros_ec_proto.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/platform/chrome/cros_ec_proto.c b/drivers/platform/chrome/cros_ec_proto.c
index f776fd42244f..cf7ef5f9db84 100644
--- a/drivers/platform/chrome/cros_ec_proto.c
+++ b/drivers/platform/chrome/cros_ec_proto.c
@@ -813,6 +813,7 @@ int cros_ec_get_next_event(struct cros_ec_device *ec_dev,
 	if (ret == -ENOPROTOOPT) {
 		dev_dbg(ec_dev->dev,
 			"GET_NEXT_EVENT returned invalid version error.\n");
+		mutex_lock(&ec_dev->lock);
 		ret = cros_ec_get_host_command_version_mask(ec_dev,
 							EC_CMD_GET_NEXT_EVENT,
 							&ver_mask);
@@ -829,6 +830,7 @@ int cros_ec_get_next_event(struct cros_ec_device *ec_dev,
 		ec_dev->mkbp_event_supported = fls(ver_mask);
 		dev_dbg(ec_dev->dev, "MKBP support version changed to %u\n",
 			ec_dev->mkbp_event_supported - 1);
+		mutex_unlock(&ec_dev->lock);
 
 		/* Try to get next event with new MKBP support version set. */
 		ret = get_next_event(ec_dev);
-- 
2.45.2.1089.g2a221341d9-goog