platform/chrome: cros_ec: Use per-device lockdep key

Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
the following lock sequences:

1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
2. lock(&ec_dev->lock); lock(prepare_lock);

The actual dependency chains are much longer. The shortened version
looks somewhat like:

1. cros-ec-rpmsg on mtk-scp
   ec_dev->lock -> prepare_lock
2. In rt5682_i2c_probe() on native I2C bus:
   prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
3. In rt5682_i2c_probe() on native I2C bus:
   regmap->lock -> i2c_adapter->bus_lock
4. In sbs_probe() on i2c-cros-ec-tunnel I2C bus attached on cros-ec:
   i2c_adapter->bus_lock -> ec_dev->lock

While lockdep is correct that the shared lockdep classes have a circular
dependency, it is bogus because

  a) 2+3 happen on a native I2C bus
  b) 4 happens on the actual EC on ChromeOS devices
  c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
     happens to expose a cros-ec interface, but does not have an
     i2c-cros-ec-tunnel I2C bus

In short, the "dependencies" are actually on different devices.

Setup a per-device lockdep key for cros_ec devices so lockdep can tell
the two instances apart. This helps with getting rid of the bogus
lockdep warning. For ChromeOS devices that only have one cros-ec
instance this doesn't change anything.

Also add a missing mutex_destroy, just to make the teardown complete.

[1] This is likely the per I2C bus lock with shared lockdep class

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20230111074146.2624496-1-wenst@chromium.org

1 files changed, 11 insertions, 3 deletions

diff --git a/drivers/platform/chrome/cros_ec.c b/drivers/platform/chrome/cros_ec.c
index c4345dafec57..b895c8130bba 100644
--- a/drivers/platform/chrome/cros_ec.c
+++ b/drivers/platform/chrome/cros_ec.c
@@ -199,12 +199,14 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
 	if (!ec_dev->dout)
 		return -ENOMEM;
 
+	lockdep_register_key(&ec_dev->lockdep_key);
 	mutex_init(&ec_dev->lock);
+	lockdep_set_class(&ec_dev->lock, &ec_dev->lockdep_key);
 
 	err = cros_ec_query_all(ec_dev);
 	if (err) {
 		dev_err(dev, "Cannot identify the EC: error %d\n", err);
-		return err;
+		goto destroy_mutex;
 	}
 
 	if (ec_dev->irq > 0) {
@@ -216,7 +218,7 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
 		if (err) {
 			dev_err(dev, "Failed to request IRQ %d: %d\n",
 				ec_dev->irq, err);
-			return err;
+			goto destroy_mutex;
 		}
 	}
 
@@ -227,7 +229,8 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
 	if (IS_ERR(ec_dev->ec)) {
 		dev_err(ec_dev->dev,
 			"Failed to create CrOS EC platform device\n");
-		return PTR_ERR(ec_dev->ec);
+		err = PTR_ERR(ec_dev->ec);
+		goto destroy_mutex;
 	}
 
 	if (ec_dev->max_passthru) {
@@ -293,6 +296,9 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
 exit:
 	platform_device_unregister(ec_dev->ec);
 	platform_device_unregister(ec_dev->pd);
+destroy_mutex:
+	mutex_destroy(&ec_dev->lock);
+	lockdep_unregister_key(&ec_dev->lockdep_key);
 	return err;
 }
 EXPORT_SYMBOL(cros_ec_register);
@@ -310,6 +316,8 @@ void cros_ec_unregister(struct cros_ec_device *ec_dev)
 	if (ec_dev->pd)
 		platform_device_unregister(ec_dev->pd);
 	platform_device_unregister(ec_dev->ec);
+	mutex_destroy(&ec_dev->lock);
+	lockdep_unregister_key(&ec_dev->lockdep_key);
 }
 EXPORT_SYMBOL(cros_ec_unregister);