linux-kernel - Re: [rfc, rft, PATCH v1 1/1] gpio: aggregator: Introduce delay support for individual output pins

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Message-ID: <ZIdWtBXLl2iJtWVF@smile.fi.intel.com>
Date:   Mon, 12 Jun 2023 20:32:36 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Alexander Stein <linux@...tq-group.com>
Subject: Re: [rfc, rft, PATCH v1 1/1] gpio: aggregator: Introduce delay
 support for individual output pins

On Fri, Jun 09, 2023 at 09:11:04AM +0200, Geert Uytterhoeven wrote:
> On Thu, Jun 8, 2023 at 6:23 PM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> > The aggregator mode can also handle properties of the platform, that
> > do not belong to the GPIO controller itself. One of such a property
> > is signal delay line. Intdoduce support of it.
> >
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > ---
> >
> > I don't like the idea of gpio-delay or similar. We have already GPIO
> > aggregator that incorporates the GPIO proxy / forwarder functionality.
> 
> I think this makes sense.

Thank you for the support of the idea.

...

> I hope no one ever needs to use the values from the example in the
> bindings
> 
>     enable-gpios = <&enable_delay 0 130000 30000>;
> 
> on a non-sleepable GPIO. Not only is a looping delay of 130 ms very bad
> for system responsiveness, such large delays may not even be supported
> on all systems (e.g. ARM implementation says < 2 ms).
> So for large values, this should use mdelay().
> 
> This also applies to gpio-delay, of course.

Thank you for pointing this out. I will think about better approach.
Shan't we add a comment into DT bindings to warn users about this?

-- 
With Best Regards,
Andy Shevchenko