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

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Date:   Thu, 15 Sep 2016 16:08:52 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        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

2016-09-15 15:39 GMT+02:00 Peter Zijlstra <peterz@...radead.org>:
> On Thu, Sep 15, 2016 at 03:20:58PM +0200, Bartosz Golaszewski wrote:
>> 2016-09-15 14:41 GMT+02:00 Linus Walleij <linus.walleij@...aro.org>:
>> >> 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?
>> >
>>
>> I think it may be more complicated than that, depending on the hw
>> topology, but the general idea seems reasonable. I'll try this.
>
> Yeah, I figured there might be more to it.
>
> In any case, if this fails, we can always punt and simply count the
> total number of instances of this driver on the system and go with that.
>

But for __mutex_init() to work with the key argument you need to know
it at compile time, right?