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authorBartosz Golaszewski <bgolaszewski@baylibre.com>2016-09-16 18:02:45 +0200
committerWolfram Sang <wsa@the-dreams.de>2016-09-24 10:53:14 +0200
commit559b46990e7635758d7350a4385d63682b181ed1 (patch)
treeb09df43deaffb3ebe44921b588b2574d6e074c9c /drivers/gpio
parent2771dc34ddaa313127d6431f23ae4cea26b869b0 (diff)
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/gpio')
-rw-r--r--drivers/gpio/gpio-pca953x.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
index 02f2a5621bb0..892dc043f40b 100644
--- a/drivers/gpio/gpio-pca953x.c
+++ b/drivers/gpio/gpio-pca953x.c
@@ -786,6 +786,8 @@ static int pca953x_probe(struct i2c_client *client,
chip->chip_type = PCA_CHIP_TYPE(chip->driver_data);
mutex_init(&chip->i2c_lock);
+ lockdep_set_subclass(&chip->i2c_lock,
+ i2c_adapter_depth(client->adapter));
/* initialize cached registers from their original values.
* we can't share this chip with another i2c master.