linux-kernel - Re: [PATCH/RFC 0/2] gpio: of: Add DT overlay support for GPIO hogs

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Message-ID: <CAMuHMdVo7bvCKjn2-SD4j7EPwDPeTWn2Sh2e-Moj+RkqudZGuQ@mail.gmail.com>
Date:   Tue, 7 Jan 2020 08:46:12 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Linus Walleij <linus.walleij@...aro.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Frank Rowand <frowand.list@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Chris Brandt <chris.brandt@...esas.com>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        linux-devicetree <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC 0/2] gpio: of: Add DT overlay support for GPIO hogs

Hi Bartosz,

On Fri, Jan 3, 2020 at 10:51 AM Bartosz Golaszewski
<bgolaszewski@...libre.com> wrote:
> pon., 30 gru 2019 o 14:38 Geert Uytterhoeven <geert+renesas@...der.be>
> napisał(a):
> > As GPIO hogs are configured at GPIO controller initialization time,
> > adding/removing GPIO hogs in Device Tree overlays currently does not
> > work.  Hence this patch series adds support for that, by registering an
> > of_reconfig notifier, as is already done for platform, i2c, and SPI
> > devices.
> >
> > Perhaps this would be better served through a pinctrl-gpio driver?
> > Pinctrl is already working fine with DT overlays, as the pinctrl-*
> > properties are part of the slave device node, and thus looked up at
> > slave device node attachment time, not at pin controller initialization
> > time.
> >
> > In my particular use case (talking to SPI devices connected to a PMOD
> > connector on the RSK+RZA1 development board), the GPIO performs board
> > level muxing of a.o. the SPI MOSI/MISO/SCK signals.  Hence the hog
> > really needs to be active only while talking to the SPI device, so the
> > muxing could (in theory) be done upon demand.
> > But how to describe that in DT, and implement it (using Runtime PM?)?
>
> I may be missing the whole picture, but from your description this
> sounds like a job for the mux framework. Maybe we could make runtime
> PM aware of muxing for this type of use-cases?

I'm happy with a (static) GPIO hog.

BTW, what exactly do you mean with "mux framework"? Pinctrl/pinmux?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds