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559b46990e
If an I2C GPIO multiplexer is driven by a GPIO provided by an expander
when there's a second expander using the same device driver on one of
the I2C bus segments, lockdep prints a deadlock warning when trying to
set the direction or the value of the GPIOs provided by the second
expander.
The below diagram presents the setup:
- - - - -
------- --------- Bus segment 1 | |
| | | |--------------- Devices
| | SCL/SDA | | | |
| Linux |-----------| I2C MUX | - - - - -
| | | | | Bus segment 2
| | | | |-------------------
------- | --------- |
| | - - - - -
------------ | MUX GPIO | |
| | | Devices
| GPIO | | | |
| Expander 1 |---- - - - - -
| | |
------------ | SCL/SDA
|
------------
| |
| GPIO |
| Expander 2 |
| |
------------
The reason for lockdep warning is that we take the chip->i2c_lock in
pca953x_gpio_set_value() or pca953x_gpio_direction_output() and then
come right back to pca953x_gpio_set_value() when the GPIO mux kicks
in. The locks actually protect different expanders, but for lockdep
both are of the same class, so it says:
Possible unsafe locking scenario:
CPU0
----
lock(&chip->i2c_lock);
lock(&chip->i2c_lock);
*** DEADLOCK ***
May be due to missing lock nesting notation
In order to get rid of the warning, retrieve the adapter nesting depth
and use it as lockdep subclass for chip->i2c_lock.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Peter Rosin <peda@axentia.se>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
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