linux-kernel - Re: [PATCH 1/4] gpiolib: add opt-out for existing drivers with static GPIO base

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Message-ID: <40531a5e-993f-4532-b071-6f233d6923f8@pengutronix.de>
Date: Wed, 15 Jan 2025 08:07:38 +0100
From: Ahmad Fatoum <a.fatoum@...gutronix.de>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Linus Walleij <linus.walleij@...aro.org>,
 Bartosz Golaszewski <brgl@...ev.pl>, Andy Whitcroft <apw@...onical.com>,
 Joe Perches <joe@...ches.com>, Dwaipayan Ray <dwaipayanray1@...il.com>,
 Lukas Bulwahn <lukas.bulwahn@...il.com>, Fabio Estevam <festevam@...il.com>,
 Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Dario Binacchi <dario.binacchi@...rulasolutions.com>,
 Haibo Chen <haibo.chen@....com>,
 Catalin Popescu <catalin.popescu@...ca-geosystems.com>,
 linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/4] gpiolib: add opt-out for existing drivers with static
 GPIO base

On 14.01.25 20:38, Andy Shevchenko wrote:
> On Tue, Jan 14, 2025 at 12:06 PM Ahmad Fatoum <a.fatoum@...gutronix.de> wrote:
>> On 14.01.25 10:49, Andy Shevchenko wrote:
>>> On Tue, Jan 14, 2025 at 12:20 AM Ahmad Fatoum <a.fatoum@...gutronix.de> wrote:
>>>>
>>>> Some drivers have had deterministic GPIO numbering for most of
>>>> their existence, e.g. the i.MX GPIO since commit 7e6086d9e54a
>>>> ("gpio/mxc: specify gpio base for device tree probe"), more than
>>>> 12 years ago.
>>>>
>>>> Reverting this to dynamically numbered will break existing setups in
>>>> the worst manner possible: The build will succeed, the kernel will not
>>>> print warnings, but users will find their devices essentially toggling
>>>> GPIOs at random with the potential of permanent damage.
>>>>
>>>> As these concerns won't go away until the sysfs interface is removed,
>>>> let's add a new struct gpio_chip::legacy_static_base member that can be
>>>> used by existing drivers that have been grandfathered in to suppress
>>>> the warning currently being printed:
>>>>
>>>>   gpio gpiochip0: Static allocation of GPIO base is deprecated,
>>>>   use dynamic allocation.
>>>
>>> Warning is harmless and still a good reminder for the stuff that needs
>>> more love.
>>> NAK.
>>
>> A warning is a call-to-action and it's counterproductive to keep tricking
>> people into removing the static base and breaking other users' scripts.
> 
> Are you prepared to say the same when the entire GPIO SYSFS will be
> removed? Because that's exactly what I referred to in the reply to the
> cover letter as an impediment to move forward.

No. But this gives me an idea: We could make the warning dependent
on CONFIG_GPIO_SYSFS and add a comment to the i.MX code suggesting
users do that instead. What do you think?

>> I don't understand what love you think this will spawn with regards
>> to the i.MX GPIO driver. Can you explain?
> 
> To fix the bugs you found. If it's not the GPIO driver a culprit, we
> need to find the real one and fix that.

Again: jumbling GPIOs with potential hardware harm as a result is not a fix.

Cheers,
Ahmad


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