linux-kernel - Re: [PATCH] Documentation: gpio: describe uAPI behaviour when hardware doesn't support requested config

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Message-ID: <CAHp75Vd1dipGkCgQBENN3rLeUO+eQfOz9uKzz86eK755smqGag@mail.gmail.com>
Date: Tue, 23 Jan 2024 17:44:52 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Kent Gibson <warthog618@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org, 
	linux-doc@...r.kernel.org, brgl@...ev.pl, linus.walleij@...aro.org, 
	andy@...nel.org, corbet@....net
Subject: Re: [PATCH] Documentation: gpio: describe uAPI behaviour when
 hardware doesn't support requested config

On Tue, Jan 23, 2024 at 3:39 PM Kent Gibson <warthog618@...il.com> wrote:
>
> The existing uAPI documentation does not adequately describe how the kernel
> handles the case where the underlying hardware or driver does not support
> the requested configuration.
>
> Add a Configuration Support section describing that behaviour to both the
> v1 and v2 documentation, and better document the errors returned where the
> requested configuration cannot be supported.

..

> +Bias             best effort

So, best effort means that in some cases it won't fail. It reminds me
of the baud rate setting in serial (TermIOS). The question here is how
does user space know that it fell in one of such cases? (In termios
the IOCTL updates the respective fields and then user space can get
settings to see what has actually been applied.)

Floating line is not good in some cases and user space really wants to
know that and treat it as an error (if needed). Hence the above Q. I
believe this needs to be explained in the documentation.

..

> +Bias             best effort

Ditto.

..

Personally I would still do two patches per ABI version, but it's up
to Bart what he wants to see at the end.

--
With Best Regards,
Andy Shevchenko