linux-kernel - Re: [PATCH v1 2/3] Documentation: gpio: Add a section on what to return in ->get() callback

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Date:   Wed, 7 Dec 2022 14:49:20 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Kent Gibson <warthog618@...il.com>, Marc Zyngier <maz@...nel.org>,
        linux-gpio@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Bartosz Golaszewski <brgl@...ev.pl>,
        Jonathan Corbet <corbet@....net>,
        Hans de Goede <hdegoede@...hat.com>
Subject: Re: [PATCH v1 2/3] Documentation: gpio: Add a section on what to
 return in ->get() callback

On Wed, Dec 7, 2022 at 10:56 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> On Wed, Dec 07, 2022 at 01:06:46AM +0100, Linus Walleij wrote:
> > On Mon, Dec 5, 2022 at 2:43 AM Kent Gibson <warthog618@...il.com> wrote:
> >
> > > My preference would be for the driver API to be extended with a new
> > > callback for the output buffer, say get_output(), and have the existing
> > > get() always return the input buffer.
> >
> > This has a certain elegance to it, as it cuts to the bone of the
> > problem and partition it in two halves, reflecting the two pieces
> > of hardware: input and output buffer. Also follows Rusty Russells
> > API hierarchy.
>
> The (one of) problem is that not all hardware may support input and output
> be enabled at the same time. What would that new API return in that case
> and how it would be better with get() returning the value depending on
> direction?

I imagine we would leave the .get_output() unassigned and the core
would just rely on whatever behaviour it has now, so in *that* case,
the implementation of .get() will need to be more elaborate.

Yours,
Linus Walleij