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

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Date:   Thu, 15 Sep 2016 14:41:35 +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 Thu, Sep 15, 2016 at 9:51 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, Sep 13, 2016 at 02:29:24PM +0200, Linus Walleij wrote:
>> 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 :(
>
> Why would this be DT or ACPI specific? Linux itself has a tree/graph of
> all busses and devices right? That's what all this drivers/base/ stuff
> is on about.
>
> So can't you walk up that and see if you encounter the exact same driver
> again?
>
> Something like:
>
>         for (nr = 0, parent = dev->parent; parent; parent = parent->parent) {
>                 if (parent->device_driver == &pca953x_driver.driver)
>                         nr++;
>         }

Oh clever. Of course.

Bartosz can you try out this approach?

Yours,
Linus Walleij