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From:   Bartosz Golaszewski <bgolaszewski@baylibre.com>
Date:   Fri, 3 Jan 2020 10:51:09 +0100
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Subject: Re: [PATCH/RFC 0/2] gpio: of: Add DT overlay support for GPIO hogs
To:     Geert Uytterhoeven <geert+renesas@glider.be>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
        Frank Rowand <frowand.list@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Peter Ujfalusi <peter.ujfalusi@ti.com>,
        Chris Brandt <chris.brandt@renesas.com>,
        linux-gpio <linux-gpio@vger.kernel.org>,
        linux-devicetree <devicetree@vger.kernel.org>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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pon., 30 gru 2019 o 14:38 Geert Uytterhoeven <geert+renesas@glider.be>
napisa=C5=82(a):
>
>         Hi all,
>
> 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?

Bart