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961a325bec
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
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.