linux-kernel - Re: [PATCH v5 09/12] gpio: aggregator: handle runtime registration of gpio_desc in gpiochip

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Message-ID: <2f02284d-2922-4bc3-ab2a-8848023019b7@bootlin.com>
Date: Wed, 7 May 2025 15:54:26 +0200
From: Thomas Richard <thomas.richard@...tlin.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Linus Walleij <linus.walleij@...aro.org>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Bartosz Golaszewski <brgl@...ev.pl>,
 Geert Uytterhoeven <geert+renesas@...der.be>, Kees Cook <kees@...nel.org>,
 Andy Shevchenko <andy@...nel.org>, linux-gpio@...r.kernel.org,
 linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com,
 DanieleCleri@...on.eu, GaryWang@...on.com.tw, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v5 09/12] gpio: aggregator: handle runtime registration of
 gpio_desc in gpiochip_fwd

On 5/7/25 15:24, Andy Shevchenko wrote:
> On Wed, May 7, 2025 at 1:10 PM Thomas Richard
> <thomas.richard@...tlin.com> wrote:
>> On 5/7/25 08:34, Andy Shevchenko wrote:
>>> On Tue, May 6, 2025 at 6:21 PM Thomas Richard
>>> <thomas.richard@...tlin.com> wrote:
> 
> ...
> 
>>>> +       /*
>>>> +        * get_direction() is called during gpiochip registration, return input
>>>> +        * direction if there is no descriptor for the line.
>>>> +        */
>>>> +       if (!test_bit(offset, fwd->valid_mask))
>>>> +               return GPIO_LINE_DIRECTION_IN;
>>>
>>> Can you remind me why we choose a valid return for invalid line? From
>>> a pure code perspective this should return an error.
>>
>> I reproduced gpiolib behavior. During gpiochip registration, we get the
>> direction of all lines. In the case the line is not valid, it is marked
>> as input if direction_input operation exists, otherwise it is marked as
>> output. [1]
>>
>> But in fact we could return an error and the core will mark the line as
>> input. Maybe ENODEV ?
> 
> I am fine with this error code, but do we have similar cases already
> in the kernel? Do they use the same or different error code(s)?

I dumped all get_direction() operations in drivers/gpio and
drivers/pinctrl and returned values are:
- GPIO_LINE_DIRECTION_OUT and GPIO_LINE_DIRECTION_IN (make sense).
- -EINVAL (for example [1]).
- -EBADE in gpiochip_get_direction() [2].
- regmap_read() return code.

But from my point of view -EINVAL and -EBADE do not match our case.

[1]
https://elixir.bootlin.com/linux/v6.15-rc5/source/drivers/gpio/gpio-cros-ec.c#L70
[2]
https://elixir.bootlin.com/linux/v6.15-rc5/source/drivers/gpio/gpiolib.c#L359

Regards,

Thomas