linux-kernel - Re: [PATCH v2 1/2] pinctrl: bcm: bcm2835: Switch to use ->add_pin

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Date:   Sat, 14 Jan 2023 12:23:49 +0100
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Florian Fainelli <f.fainelli@...il.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>
Subject: Re: [PATCH v2 1/2] pinctrl: bcm: bcm2835: Switch to use
 ->add_pin_ranges()

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@gmail.com/
>>
>> [2] - https://lore.kernel.org/linux-arm-kernel/75266ed1-666a-138b-80f1-ae9a06b7bdf3@i2se.com/
>>
>>> 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.