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Groups > linux.kernel > #1487817
| From | Wolfram Sang <wsa@the-dreams.de> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v2 4/4] gpio: pca953x: fix an incorrect lockdep warning |
| Date | 2016-09-21 07:50 +0200 |
| Message-ID | <sjIzT-4Vo-9@gated-at.bofh.it> (permalink) |
| References | <si3S9-6Ya-3@gated-at.bofh.it> <si3S9-6Ya-9@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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On Fri, Sep 16, 2016 at 06:02:45PM +0200, Bartosz Golaszewski wrote: > 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> Linus, we'd like that in 4.9. Can I get your ack for the gpio part?
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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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