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author | Bartosz Golaszewski <bgolaszewski@baylibre.com> | 2016-09-16 16:02:45 (GMT) |
---|---|---|
committer | Wolfram Sang <wsa@the-dreams.de> | 2016-09-24 08:53:14 (GMT) |
commit | 559b46990e7635758d7350a4385d63682b181ed1 (patch) | |
tree | b09df43deaffb3ebe44921b588b2574d6e074c9c /drivers/i2c/busses/i2c-i801.c | |
parent | 2771dc34ddaa313127d6431f23ae4cea26b869b0 (diff) | |
download | linux-559b46990e7635758d7350a4385d63682b181ed1.tar.xz |
gpio: pca953x: fix an incorrect lockdep warning
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>
Diffstat (limited to 'drivers/i2c/busses/i2c-i801.c')
0 files changed, 0 insertions, 0 deletions