Re: [PATCH v2 1/2] pinctrl: bcm: bcm2835: Switch to use ->add_pin_ranges()

[Stefan Wahren]

Hi Andy,

Am 13.01.23 um 22:31 schrieb Andy Shevchenko:
> On Fri, Jan 13, 2023 at 09:13:23PM +0100, Stefan Wahren wrote:
> > Am 13.01.23 um 18:10 schrieb Andy Shevchenko:
> ...
>
> > > v2: fixed compilation issues (LKP), Cc'ed to the author of original code
> > >
> > > Btw, the commit d2b67744fd99 ("pinctrl: bcm2835: implement hook for
> > > missing gpio-ranges") seems problematic in the fist place due to
> > > odd of_node_put() call. I dunno how that part had been tested, or
> > > how it's supposed to work, i.e. where is the counterpart of_node_get().
> > > Anyway this change drops it for good.
> > The countpart is in of_pinctrl_get(). I was just following the pattern like
> > in other drivers like gpio-rockchip. The original commit has been tested by
> > Florian Fainelli and me. I'm not sure if it's safe to drop it completely.
> Please, elaborate how of_pinctrl_get() increases refcount of the parameter.
> Maybe I'm looking into a wrong place?
>
> > Btw this is not the only platform affected by the gpio-ranges compatibility
> > issue [1].
> This is the only one that uses unnecessary added callback.

i didn't have access to any of the other platforms which were also 
affected. So i thought providing a general solution would be good idea. 
I wasn't aware of add_pin_ranges().

Since i was annoyed that nobody cared about DTB backward compatibility, 
i send out a RFC series to fix the GPIO hog regression which breaks the 
LEDs on the Raspberry Pi. Nobody complained about it.

> > > Perhaps we can check gpio-ranges property presence inside the GPIO
> > > library, so this ->add_pin_ranges() won't be called at all.
> > I thought this could be very platform specific, so i implemented a hook. But
> > yes my initial hack modified gpiolib-of [2].
> The point is that possibly documentation of ->add_pin_ranges() should be
> amended to take care of the cases like this. We don't need two or more
> hooks to do the same, esp. taking into account that OF specific doesn't
> cover other cases.
>
> > [1] - https://patchwork.kernel.org/project/linux-arm-msm/patch/20180412190138.12372-1-chunkeey@xxxxxxxxx/
> >
> > [2] - https://lore.kernel.org/linux-arm-kernel/75266ed1-666a-138b-80f1-ae9a06b7bdf3@xxxxxxxx/
> >
> > > Also I would like to understand the dance around checking for pin
> > > control device. The original commit lacks of comments in the non-trivial
> > > code.
> Any comment on this?
Do you mean the NULL check? of_pinctrl_get() could return NULL, but 
pinctrl_dev_get_devname() directly access the dev member.