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

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Message-ID: <CAMpxmJX3_ec44Z0UVTNqSDjmNq+Oe3sk+szLE-Nj7X4pztbywQ@mail.gmail.com>
Date:   Sun, 18 Sep 2016 21:45:01 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Peter Rosin <peda@...ntia.se>
Cc:     Wolfram Sang <wsa@...-dreams.de>,
        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>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        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

2016-09-18 21:43 GMT+02:00 Bartosz Golaszewski <bgolaszewski@...libre.com>:
> 2016-09-18 10:52 GMT+02:00 Peter Rosin <peda@...ntia.se>:
>> On 2016-09-16 19:58, Wolfram Sang wrote:
>>>
>>> Same here. And if it prevents us from false positive lockdep reports, I
>>> am all for fixing it.
>>
>> Except it doesn't, when I think some more about it...
>>
>> If you have two gpio-expanders on the same depth but on different i2c
>> branches you still end up with a splat if one is used to control a mux
>> to reach the other.
>>
>> The only way to solve it for good, that I see, is to have every instance
>> of the gpio-expander mutex in its own class. That might lead to many
>> lockdep classes but then again, how many gpio expanders could there be
>> in a system? A dozen or two seems extreme, so maybe that is the correct
>> approach anyway?
>
> Wouldn't it be enough to have a separate class for every base (as in:
> not having any parent adapters) i2c adapter?
>

Eeek -ESENTTOOEARLY

Of course not - since we could have two branches deeper on the tree
with the same problem.

Nevermind my last e-mail.

Best regards,
Bartosz Golaszewski