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

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Message-ID: <153115064295.143105.5291742668895542720@swboyd.mtv.corp.google.com>
Date:   Mon, 09 Jul 2018 08:37:22 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Linus Walleij <linus.walleij@...aro.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()

Quoting Linus Walleij (2018-07-09 06:54:01)
> 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.
> 

Ok. Is my interpretation correct though? The fundamental question here
is if gpio_request() should remux the GPIO for the GPIO function or if
drivers are expected to have pinmux settings to use their pin as a GPIO.