linux-kernel - Re: [RFC v2 0/2] gpio: Support for shared GPIO lines on boards

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Message-ID: <20191030141736.GN4568@sirena.org.uk>
Date:   Wed, 30 Oct 2019 14:17:36 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Tero Kristo <t-kristo@...com>,
        Maxime Ripard <mripard@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        devicetree@...r.kernel.org
Subject: Re: [RFC v2 0/2] gpio: Support for shared GPIO lines on boards

On Wed, Oct 30, 2019 at 03:32:09PM +0200, Peter Ujfalusi wrote:
> On 30/10/2019 15.12, Rob Herring wrote:

> > Why can't we just add a shared flag like we have for interrupts?
> > Effectively, we have that for resets too, it's just hardcoded in the
> > the drivers.

> This would be kind of the same thing what the
> GPIOD_FLAGS_BIT_NONEXCLUSIVE does, which was a quick workaround for
> fixed-regulators afaik.

The theory with that was that any usage of this would need the
higher level code using the GPIO to cooperate so they didn't step
on each other's toes so the GPIO code should just punt to it.

> But let's say that a board design will pick two components (C1 and C2)
> and use the same GPIO line to enable them. We already have the drivers
> for them and they are used in boards already.

This is basically an attempt to make a generic implementation of
that cooperation for simple cases.

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