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

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Date:   Tue, 5 Nov 2019 10:58:03 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Peter Ujfalusi <peter.ujfalusi@...com>,
        Mark Brown <broonie@...nel.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>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [RFC v2 0/2] gpio: Support for shared GPIO lines on boards

On Mon, Nov 4, 2019 at 8:11 PM Rob Herring <robh+dt@...nel.org> wrote:
> [Peter]
> > The device needs the RST line to be high, otherwise it is not
> > accessible. If it does not have reset control how can we make sure that
> > the GPIO line is in correct state?
>
> Just like the reset code, drivers register their use of the reset and
> the core tracks users and prevents resetting when not safe. Maybe the
> reset subsystem needs to learn about GPIO resets. (...)

I agree. Certainly the reset subsystem can do what the regulator
subsystem is already doing: request the GPIO line nonexclusive
and handle any reference counting and/or quirks that are needed
in a hypothetical drivers/reset/reset-gpio.c driver.

There is no such driver today, just a "reset" driver in
drivers/power/reset that resets the whole system.

But I see no problem in creating a proper reset driver in drivers/reset
to handle a few peripherals with a shared GPIO reset line.

Yours,
Linus Walleij