linux-kernel - Re: [PATCH v2 0/4] gpio: fix an incorrect lockdep warning

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Date:   Sat, 17 Sep 2016 03:19:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Vignesh R <vigneshr@...com>, Yong Li <yong.b.li@...el.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Ingo Molnar <mingo@...hat.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Peter Rosin <peda@...ntia.se>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [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.

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

> Note: if this series gets merged, I'll prepare follow-up patches for
> other expanders for which a similar problem could potentially occur.

We can't push this annotation into the i2c core, can we? Since the mutex
is in driver specific code, not more generic...