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

diff --git a/drivers/platform/chrome/cros_ec.c b/drivers/platform/chrome/cros_ec.c
index c4345da..b895c81 100644 (file)
--- 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);
 

diff --git a/include/linux/platform_data/cros_ec_proto.h b/include/linux/platform_data/cros_ec_proto.h
index 4865c54..4f9f756 100644 (file)
--- a/include/linux/platform_data/cros_ec_proto.h
+++ b/include/linux/platform_data/cros_ec_proto.h
@@ -9,6 +9,7 @@
 #define __LINUX_CROS_EC_PROTO_H
 
 #include <linux/device.h>
+#include <linux/lockdep_types.h>
 #include <linux/mutex.h>
 #include <linux/notifier.h>
 
@@ -122,6 +123,8 @@ struct cros_ec_command {
  *            command. The caller should check msg.result for the EC's result
  *            code.
  * @pkt_xfer: Send packet to EC and get response.
+ * @lockdep_key: Lockdep class for each instance. Unused if CONFIG_LOCKDEP is
+ *              not enabled.
  * @lock: One transaction at a time.
  * @mkbp_event_supported: 0 if MKBP not supported. Otherwise its value is
  *                        the maximum supported version of the MKBP host event
@@ -176,6 +179,7 @@ struct cros_ec_device {
                        struct cros_ec_command *msg);
        int (*pkt_xfer)(struct cros_ec_device *ec,
                        struct cros_ec_command *msg);
+       struct lock_class_key lockdep_key;
        struct mutex lock;
        u8 mkbp_event_supported;
        bool host_sleep_v1;