Re: [REGRESSION] gpio hogging fails with pinctrl gpio drivers

Re: [REGRESSION] gpio hogging fails with pinctrl gpio drivers

[Linus Walleij]

On Thu, Feb 6, 2020 at 6:33 PM Russell King - ARM Linux admin
<linux@armlinux.org.uk> wrote:

> It seems that sometime between 4.20 and 5.5, something has broken the
> ability to specify gpio-hogs in DT for GPIOs that are written around
> pinctrl drivers.
(explanation that makes perfect sense)
> Consequently, adding a gpio-hog to DT for this driver results in the
> driver endlessly returning -EPROBE_DEFER.

I suspect this is sx150x-specific and suspect these two commits:

1a1d39e1b8dd pinctrl: sx150x: Register pinctrl before adding the gpiochip
b930151e5b55 pinctrl: sx150x: Add a static gpio/pinctrl pin range mapping

I suppose people weren't using hogs very much with the sx150x and
it didn't turn up in testing so far.

I don't think for example pinctrl-stmfx.c has this problem, as it registers
the pin ranges from the device tree as part of the core code.
But other drivers calling gpiochip_add_pin_range() may be experiencing
this.

Peter/Andrey, do you have some idea? Have you tested this usecase (hogs)
with the sx150x?

Yours,
Linus Walleij

Re: [REGRESSION] gpio hogging fails with pinctrl gpio drivers

[Peter Rosin]

On 2020-02-20 09:17, Linus Walleij wrote:
> On Thu, Feb 6, 2020 at 6:33 PM Russell King - ARM Linux admin
> <linux@armlinux.org.uk> wrote:
> 
>> It seems that sometime between 4.20 and 5.5, something has broken the
>> ability to specify gpio-hogs in DT for GPIOs that are written around
>> pinctrl drivers.
> (explanation that makes perfect sense)
>> Consequently, adding a gpio-hog to DT for this driver results in the
>> driver endlessly returning -EPROBE_DEFER.
> 
> I suspect this is sx150x-specific and suspect these two commits:
> 
> 1a1d39e1b8dd pinctrl: sx150x: Register pinctrl before adding the gpiochip
> b930151e5b55 pinctrl: sx150x: Add a static gpio/pinctrl pin range mapping
> 
> I suppose people weren't using hogs very much with the sx150x and
> it didn't turn up in testing so far.
> 
> I don't think for example pinctrl-stmfx.c has this problem, as it registers
> the pin ranges from the device tree as part of the core code.
> But other drivers calling gpiochip_add_pin_range() may be experiencing
> this.
> 
> Peter/Andrey, do you have some idea? Have you tested this usecase (hogs)
> with the sx150x?

I have never created gpio hogs myself, so no, I haven't done any testing
with that. Sorry. I could of course spend some time looking at this, but I
don't know all that much about the wrinkles of the interactions between
pinctrl och gpio. Or plain gpio/pinctrl for that matter. Sure, I extended
this driver, but I haven't really looked at those sub-systems since. I
think others will come up with a solution for this with much less effort
and with less risk of introducing new problems...

Cheers,
Peter

Re: [REGRESSION] gpio hogging fails with pinctrl gpio drivers

[Andrey Smirnov]

On Thu, Feb 20, 2020 at 12:18 AM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Thu, Feb 6, 2020 at 6:33 PM Russell King - ARM Linux admin
> <linux@armlinux.org.uk> wrote:
>
> > It seems that sometime between 4.20 and 5.5, something has broken the
> > ability to specify gpio-hogs in DT for GPIOs that are written around
> > pinctrl drivers.
> (explanation that makes perfect sense)
> > Consequently, adding a gpio-hog to DT for this driver results in the
> > driver endlessly returning -EPROBE_DEFER.
>
> I suspect this is sx150x-specific and suspect these two commits:
>
> 1a1d39e1b8dd pinctrl: sx150x: Register pinctrl before adding the gpiochip
> b930151e5b55 pinctrl: sx150x: Add a static gpio/pinctrl pin range mapping
>
> I suppose people weren't using hogs very much with the sx150x and
> it didn't turn up in testing so far.
>
> I don't think for example pinctrl-stmfx.c has this problem, as it registers
> the pin ranges from the device tree as part of the core code.
> But other drivers calling gpiochip_add_pin_range() may be experiencing
> this.
>
> Peter/Andrey, do you have some idea? Have you tested this usecase (hogs)
> with the sx150x?
>

Haven't done any GPIO hogging on sx150x, unfortunately. My use-cases were:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/vf610-zii-dev-rev-c.dts

and

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/vf610-zii-scu4-aib.dts

which didn't have any hogs so far (there's a chance Russell is using
the former for his experiments, so maybe that'll change). I don't any
useful input on this regression, sorry. I do have Rev C. board readily
available, so I can provide Tested-by's if I am CC'd on fixes.

Thanks,
Andrey Smirnov

Re: [REGRESSION] gpio hogging fails with pinctrl gpio drivers

[Russell King - ARM Linux admin]

On Thu, Feb 20, 2020 at 09:28:14AM -0800, Andrey Smirnov wrote:
> On Thu, Feb 20, 2020 at 12:18 AM Linus Walleij <linus.walleij@linaro.org> wrote:
> >
> > On Thu, Feb 6, 2020 at 6:33 PM Russell King - ARM Linux admin
> > <linux@armlinux.org.uk> wrote:
> >
> > > It seems that sometime between 4.20 and 5.5, something has broken the
> > > ability to specify gpio-hogs in DT for GPIOs that are written around
> > > pinctrl drivers.
> > (explanation that makes perfect sense)
> > > Consequently, adding a gpio-hog to DT for this driver results in the
> > > driver endlessly returning -EPROBE_DEFER.
> >
> > I suspect this is sx150x-specific and suspect these two commits:
> >
> > 1a1d39e1b8dd pinctrl: sx150x: Register pinctrl before adding the gpiochip
> > b930151e5b55 pinctrl: sx150x: Add a static gpio/pinctrl pin range mapping
> >
> > I suppose people weren't using hogs very much with the sx150x and
> > it didn't turn up in testing so far.
> >
> > I don't think for example pinctrl-stmfx.c has this problem, as it registers
> > the pin ranges from the device tree as part of the core code.
> > But other drivers calling gpiochip_add_pin_range() may be experiencing
> > this.
> >
> > Peter/Andrey, do you have some idea? Have you tested this usecase (hogs)
> > with the sx150x?
> >
> 
> Haven't done any GPIO hogging on sx150x, unfortunately. My use-cases were:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/vf610-zii-dev-rev-c.dts
> 
> and
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/vf610-zii-scu4-aib.dts
> 
> which didn't have any hogs so far (there's a chance Russell is using
> the former for his experiments, so maybe that'll change). I don't any
> useful input on this regression, sorry. I do have Rev C. board readily
> available, so I can provide Tested-by's if I am CC'd on fixes.

The ZII dev rev C is where I had the hog as a means of kicking the
88x3310 PHY out of reset.

I've now converted it to a proper MDIO bus-level reset, so I no
longer have the hog, and I no longer care about the regression - but
that's not to say it shouldn't be fixed, as the code is wrong.

-- 
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