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

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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
This commit is contained in:
Chen-Yu Tsai 2023-01-11 15:41:46 +08:00 committed by Tzung-Bi Shih
parent 5fa1dd818f
commit 961a325bec
2 changed files with 15 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

14
drivers/platform/chrome/cros_ec.c
View file

@ -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);

4
include/linux/platform_data/cros_ec_proto.h
View file

@ -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;