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Groups > linux.kernel > #1485148
| From | Bartosz Golaszewski <bgolaszewski@baylibre.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH v2 4/4] gpio: pca953x: fix an incorrect lockdep warning |
| Date | 2016-09-16 18:10 +0200 |
| Message-ID | <si3S9-6Ya-9@gated-at.bofh.it> (permalink) |
| References | <si3S9-6Ya-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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(+)
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.
--
2.7.4
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[PATCH v2 4/4] gpio: pca953x: fix an incorrect lockdep warning Bartosz Golaszewski <bgolaszewski@baylibre.com> - 2016-09-16 18:10 +0200
Re: [PATCH v2 4/4] gpio: pca953x: fix an incorrect lockdep warning Wolfram Sang <wsa@the-dreams.de> - 2016-09-21 07:50 +0200
Re: [PATCH v2 4/4] gpio: pca953x: fix an incorrect lockdep warning Linus Walleij <linus.walleij@linaro.org> - 2016-09-23 10:20 +0200
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