From: Chen-Yu Tsai wenst@chromium.org

[ Upstream commit 961a325becd9a142ae5c8b258e5c2f221f8bfac8 ]

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 Stable-dep-of: e23749534619 ("platform/chrome: cros_ec: Unregister notifier in cros_ec_unregister()") Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/platform/chrome/cros_ec.c | 14 +++++++++++--- include/linux/platform_data/cros_ec_proto.h | 4 ++++ 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/chrome/cros_ec.c b/drivers/platform/chrome/cros_ec.c index ec733f683f34..4ae57820afd5 100644 --- a/drivers/platform/chrome/cros_ec.c +++ b/drivers/platform/chrome/cros_ec.c @@ -198,12 +198,14 @@ 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) { @@ -215,7 +217,7 @@ 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; } }

@@ -226,7 +228,8 @@ 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) { @@ -292,6 +295,9 @@ 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); @@ -309,6 +315,8 @@ 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 e43107e0bee1..2bf307e74490 100644 --- 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>

@@ -116,6 +117,8 @@ 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 @@ -160,6 +163,7 @@ 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;