linux-kernel - Re: [PATCH v4] gpio: Return EPROBE_DEFER if gc->to

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Message-ID: <87v8xmxkg7.fsf@collabora.com>
Date:   Thu, 10 Feb 2022 20:26:16 -0500
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Shreeya Patel <shreeya.patel@...labora.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        wsa@...nel.org, kernel@...labora.com,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        kbuild test robot <lkp@...el.com>
Subject: Re: [PATCH v4] gpio: Return EPROBE_DEFER if gc->to_irq is NULL

Bartosz Golaszewski <brgl@...ev.pl> writes:

> My email address changed in September, that's why I didn't see the
> email you sent in November to my old one.

Hi Bart,

thanks for the prompt reply and sorry for the wrong email address.

> gpiod_to_irq() can be used in context other than driver probing, I'm
> worried existing users would not know how to handle it. Also: how come
> you can get the GPIO descriptor from the provider but its interrupts
> are not yet set up?

I'm definitely some context here, as its been quite a while.
Shreeya, feel free to pitch in. :)

This is one of the races we saw in gpiochip_add_irqchip, depending on
the probe order.  The gc is already visible while partially initialized,
if pinctrl-amd hasn't been probed yet.  Another device being probed can
hit an -ENXIO here if to_irq is yet uninitialized or enter .to_irq() and
oops.  Shreeya's patch workarounds the first issue, but is not a
solution for the second.

There is another patch that has been flying around to address the Oops.

https://lkml.org/lkml/2021/11/8/900

She's been working on a proper solution for that one, which might
actually address this too and replace the current patch.  Maybe you
could help us get to a proper solution there?  I'm quite unfamiliar with
this code myself :)

-- 
Gabriel Krisman Bertazi