| Message ID | 1474041765-17818-5-git-send-email-bgolaszewski@baylibre.com |
|---|---|
| State | New |
| Headers | show |
On Wed, Sep 21, 2016 at 7:45 AM, Wolfram Sang <wsa@the-dreams.de> wrote: >> 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> > > Linus, we'd like that in 4.9. Can I get your ack for the gpio part? Acked-by: Linus Walleij <linus.walleij@linaro.org> Sorry for not attending quick enough, I was down in the block layer. Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c index 02f2a56..892dc04 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.
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> --- drivers/gpio/gpio-pca953x.c | 2 ++ 1 file changed, 2 insertions(+) -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html