linux-kernel - Re: [PATCH 2/3] pinctrl: msm: Mux out gpio function with gpio

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Message-ID: <CACRpkdbNSNzT8tiYDXk1dc447xGqf1bV+O93hgEQdT+GcQtddA@mail.gmail.com>
Date:   Mon, 9 Jul 2018 15:54:01 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Doug Anderson <dianders@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 2/3] pinctrl: msm: Mux out gpio function with gpio_request()

On Mon, Jul 2, 2018 at 7:56 PM Stephen Boyd <swboyd@...omium.org> wrote:

> I could do with some more clarity from Linus in the "Drivers needing
> both pin control and GPIOs" section of
> Documentation/driver-api/pinctl.rst but I read that section as stating
> that the GPIO driver needs to mux the pin as a GPIO by requesting the
> pinctrl backend to do so, unless the hardware overrides the muxed
> function selection when the GPIO is used, without involving pinctrl
> software.

Yeah that text is especially terse :/

What it says (or what I meant to say) is that there is a choice
between letting the pin control and GPIO functionality on the
same pin be handled orthogonally or implementing these
gpio_*() callbacks into the pin control backend, but in either case
the two APIs must be used in sequence:
pin control setting comes first, second the GPIO subsystem can
request the GPIO line.

I'll see if I can clarify.

Yours,
Linus Walleij