linux-kernel - Re: lockdep: incorrect deadlock warning with two GPIO expanders

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Message-ID: <CACRpkdb00e=YexmCRwv=evVLjBDM6Pjqtcs+Mnc8JVD1Ssa5mA@mail.gmail.com>
Date:   Tue, 13 Sep 2016 14:29:24 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Alexandre Courbot <gnurou@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-gpio <linux-gpio@...r.kernel.org>
Subject: Re: lockdep: incorrect deadlock warning with two GPIO expanders

On Mon, Sep 12, 2016 at 5:33 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Sep 12, 2016 at 05:16:14PM +0200, Bartosz Golaszewski wrote:

>> AFAIK there is no clean way to tell that a GPIO is used by an I2C
>> multiplexer at probe time. Linus, Alexandre could you confirm?

Nominally, the GPIO descriptors are just abstract resources such
as regulators or clocks, they can be used for a lot but just like
a clock, regulator, dma channel etc does not know who is using
it and for what, it does not know this, no.

> You cannot inspect the device tree while probing?

Of course it *can* but we would end up encoding a special
case every time something like this happens, tied to just
device tree, then another bolt-on for ACPI etc.

I have a hard time following the problem really, I'm
afraid I'm simply just not smart enough :(

Yours,
Linus Walleij