Re: [PATCH] gpio: Revert regression in sysfs-gpio (gpiolib.c)

[Marcelo Roberto Jimenez <marcelo.jimenez@xxxxxxxxx>]

Hi,

On Mon, Jan 10, 2022 at 4:02 AM Thorsten Leemhuis
<regressions@xxxxxxxxxxxxx> wrote:
>
> Hi, this is your Linux kernel regression tracker speaking.
>
> On 20.12.21 21:41, Marcelo Roberto Jimenez wrote:
> > On Mon, Dec 20, 2021 at 11:57 AM Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
> >> On Sat, Dec 18, 2021 at 7:28 AM Thorsten Leemhuis
> >> <regressions@xxxxxxxxxxxxx> wrote:
> >>>
> >>> [TLDR: I'm adding this regression to regzbot, the Linux kernel
> >>> regression tracking bot; most text you find below is compiled from a few
> >>> templates paragraphs some of you might have seen already.]
> >>>
> >>> On 17.12.21 16:35, Marcelo Roberto Jimenez wrote:
> >>>> Some GPIO lines have stopped working after the patch
> >>>> commit 2ab73c6d8323f ("gpio: Support GPIO controllers without pin-ranges")
> >>>>
> >>>> And this has supposedly been fixed in the following patches
> >>>> commit 89ad556b7f96a ("gpio: Avoid using pin ranges with !PINCTRL")
> >>>> commit 6dbbf84603961 ("gpiolib: Don't free if pin ranges are not defined")
> >>>
> >>> There seems to be a backstory here. Are there any entries and bug
> >>> trackers or earlier discussions everyone that looks into this should be
> >>> aware of?
> >>
> >> Agreed with Thorsten. I'd like to first try to determine what's wrong
> >> before reverting those, as they are correct in theory but maybe the
> >> implementation missed something.
> >>
> >> Have you tried tracing the execution on your platform in order to see
> >> what the driver is doing?
> >
> > Yes. The problem is that there is no list defined for the sysfs-gpio
> > interface. The driver will not perform pinctrl_gpio_request() and will
> > return zero (failure).
> >
> > I don't know if this is the case to add something to a global DTD or
> > to fix it in the sysfs-gpio code.
>
> Out of interest, has any progress been made on this front?
>
> BTW, there was a last-minute commit for 5.16 yesterday that referenced
> the culprit Marcelo specified:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=master&id=c8013355ead68dce152cf426686f8a5f80d88b40
>
> This was for a BCM283x and BCM2711 devices, so I assume it won't help.
> Wild guess (I don't know anything about this area of the kernel):
> Marcelo, do the dts files for your hardware maybe need a similar fix?

I have tried to add "gpio-ranges" to the gpio-controllers in
at91sam9x5.dtsi, but the system deadlocks, because in pinctrl-at91.c,
function at91_pinctrl_probe() we have:

/*
* We need all the GPIO drivers to probe FIRST, or we will not be able
* to obtain references to the struct gpio_chip * for them, and we
* need this to proceed.
*/
for (i = 0; i < gpio_banks; i++)
        if (gpio_chips[i])
                ngpio_chips_enabled++;

        if (ngpio_chips_enabled < info->nactive_banks) {
                dev_warn(&pdev->dev,
                      "All GPIO chips are not registered yet (%d/%d)\n",
                      ngpio_chips_enabled, info->nactive_banks);
               devm_kfree(&pdev->dev, info);
                return -EPROBE_DEFER;
        }

On the other hand, in gpiolib-of.c, function
of_gpiochip_add_pin_range() we have:

if (!pctldev)
        return -EPROBE_DEFER;

In other words, the pinctrl needs all the gpio-controllers, and the
gpio-controllers need the pinctrl. Each returns -EPROBE_DEFER and the
system deadlocks.

>
> Ciao, Thorsten
>
> P.S.: As a Linux kernel regression tracker I'm getting a lot of reports
> on my table. I can only look briefly into most of them. Unfortunately
> therefore I sometimes will get things wrong or miss something important.
> I hope that's not the case here; if you think it is, don't hesitate to
> tell me about it in a public reply, that's in everyone's interest.
>
> BTW, I have no personal interest in this issue, which is tracked using
> regzbot, my Linux kernel regression tracking bot
> (https://linux-regtracking.leemhuis.info/regzbot/). I'm only posting
> this mail to get things rolling again and hence don't need to be CC on
> all further activities wrt to this regression.
>
> #regzbot poke
>

Regards,
Marcelo.