linux-kernel - Re: [PATCH 3/3] gpio: Add reference counting for non-exclusive GPIOs

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Message-ID: <20181123132522.GE2089@sirena.org.uk>
Date:   Fri, 23 Nov 2018 13:25:22 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Charles Keepax <ckeepax@...nsource.cirrus.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        patches@...nsource.cirrus.com
Subject: Re: [PATCH 3/3] gpio: Add reference counting for non-exclusive GPIOs

On Fri, Nov 23, 2018 at 10:57:29AM +0000, Charles Keepax wrote:

> It's fixing something in the case of two regulators using the
> same GPIO. The direction this patch chain takes is that the end
> drivers own the GPIOs not the regulator core (except for the
> legacy case). So both of the end drivers will devm_ request their

The situation with descriptor based GPIOs is a bug - the reason why the
core does the request in the legacy case is precisely the problem Linus
identified.  Once a GPIO is shared all the users of the GPIO need to
coordinate with each other in order to set the value so the refcount by
itself in the GPIO core isn't super useful unless it can also serve to
help the multiple users find each other somehow.  I think what we want
to do here is either push the gpiod requests into the regulator core or
change things so that once the regulator is registered with the
regulator core the regulator core owns and is responsible for freeing
the regulator.

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