Re: Linux 5.17-rc8

[Bartosz Golaszewski <brgl@bgdev.pl>]

On Tue, Mar 15, 2022 at 2:47 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Mon, Mar 14, 2022 at 5:45 PM Marcelo Roberto Jimenez
> <marcelo.jimenez@gmail.com> wrote:
> >
> > At a certain point, I tried Thorsten's suggestion to add a gpio-ranges
> > property in a way similar to another patch, but the kernel went into
> > an EPROBE_DEFER deadlock. Thierry Reding made some comments about this
> > in the sequence.
>
> Hmm. The problem does sound like that particular driver doesn't use
> the pin_ranges thing, so then the tests for an empty pin_ranges will
> always be true.
>
> The EPROBE_DEFER deadlock then sounds like something went wrong in the
> gpio-ranges patch when you tried to fix it - but I don't actually find
> that patch or that attempt, so I can't even guess at it.
>
> This whole code pin_ranges code looks very odd:
> gpiochip_add_pin{group}_range() seems to add the pin ranges properly,
> but that actual gpiochip_add_pin_ranges() function does *not*.
>
> It just expects that that the 'add_pin_ranges()' callback exists, and
> if it doesn't, does nothing at all.
>
> Which then makes those
>
>         if (list_empty(&gc->gpiodev->pin_ranges))
>                 return 0;
>
> tests very suspicious - because if some doesn't implement that
> add_pin_ranges() callback, it looks like nothing at all ever gets
> done, because nothing calls the function to actually add the pinrange.
> And then that "list_empty()" test very much will trigger.
>
> IOW, it looks like either a gpio controller has to implement that
> 'add_pin_ranges()' function (only tegra), or it needs to always add
> the pin ranges at probe time.
>
> Am I guessing right that the driver that you use does neither?
>

There are more drivers than just tegra that implement add_pin_ranges()
but you're right, pinctrl-at91.c used by Marcelo does not.

> LinusW/Bartoz - this all really sounds strange to me. Maybe I'm

It's BartoSz actually. :)

> misreading the situation entirely. Should there be some sanity-test
> that any gpio/pinctrl driver that uses gpiochip_generic_request()
> would either have to have that add_pin_ranges() callback, or a
> successful probe needs to always populate that 'gpiodev->pin_ranges'
> list?
>

This sounds right to me but I need to spend some more time on this, I
didn't author the code in question.

> Or maybe I'm misreading the situation entirely. I don't know the code
> - I'm just grepping for things and trying to make sense of how that
> '->pin_ranges' list is supposed to work.
>
> But for now, I think that patch has to be reverted.
>

Sounds good, I'll send a revert and make another PR with fixes before v5.17.

Bartosz

>                Linus