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SubjectRe: [PATCH v2 0/4] gpio: fix an incorrect lockdep warning
On Fri, Sep 16, 2016 at 06:02:41PM +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.
>
> This series exports an already existing function from i2c-core as
> public API and reuses it in pca953x to pass a correct lock subclass
> to lockdep.
>
> Note: if this series gets merged, I'll prepare follow-up patches for
> other expanders for which a similar problem could potentially occur.
>
> Tested with the following setup:
>
> ------- --------- Bus segment 1 | |
> | | | |--------------- Devices
> | | SCL/SDA | | | |
> | Linux |-----------| I2C MUX | - - - - -
> | | | | | Bus segment 2
> | | | | |-------------------
> ------- | --------- |
> | | - - - - -
> ------------ | MUX GPIO | |
> | | | Devices
> | GPIO | | | |
> | Expander 1 |---- - - - - -
> | | |
> ------------ | SCL/SDA
> |
> ------------
> | |
> | GPIO |
> | Expander 2 |
> | |
> ------------
>
> where expander 1 is a pca9534 and expander 2 is a pca9535.
>
> v1 -> v2:
> - added patches 1/4, 2/4 & 3/4
> - used i2c_adapter_depth() in patch 4/4 in order to detect multiple
> adapter nesting
>
> Bartosz Golaszewski (4):
> i2c: export i2c_adapter_depth()
> lockdep: make MAX_LOCKDEP_SUBCLASSES unconditionally visible
> i2c: add a warning to i2c_adapter_depth()
> gpio: pca953x: fix an incorrect lockdep warning

Applied to for-next, thanks!

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