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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Thu, 25 Nov 2021 08:58:13 +0100
Message-ID: <CAMuHMdV5sjVg6BEm3zgvvsJDHJwKP1A8rh-sama8suCG5SYQyA@mail.gmail.com>
Subject: Re: [PATCH v8 6/8] MIPS: DTS: CI20: Add DT nodes for HDMI setup
To:     "H. Nikolaus Schaller" <hns@goldelico.com>
Cc:     Paul Cercueil <paul@crapouillou.net>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Kees Cook <keescook@chromium.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Robert Foss <robert.foss@linaro.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        Harry Wentland <harry.wentland@amd.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Maxime Ripard <maxime@cerno.tech>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Paul Boddie <paul@boddie.org.uk>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        letux-kernel@openphoenux.org, Jonas Karlman <jonas@kwiboo.se>,
        DRI Development <dri-devel@lists.freedesktop.org>
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Hi Nikolaus,

On Wed, Nov 24, 2021 at 5:31 PM H. Nikolaus Schaller <hns@goldelico.com> wrote:
> > Am 24.11.2021 um 17:21 schrieb Geert Uytterhoeven <geert@linux-m68k.org>:
> > On Wed, Nov 24, 2021 at 5:19 PM H. Nikolaus Schaller <hns@goldelico.com> wrote:
> >>> Am 23.11.2021 um 21:10 schrieb Paul Cercueil <paul@crapouillou.net>:
> >>> Le mar., nov. 23 2021 at 19:13:59 +0100, H. Nikolaus Schaller <hns@goldelico.com> a écrit :
> >>>> +    assigned-clock-rates = <48000000>, <0>, <54000000>, <0>, <27000000>;
> >>>> };
> >>>> &tcu {
> >>>> @@ -509,6 +534,19 @@ pins_i2c4: i2c4 {
> >>>>             bias-disable;
> >>>>     };
> >>>> +    pins_hdmi_ddc: hdmi_ddc {
> >>>> +            function = "hdmi-ddc";
> >>>> +            groups = "hdmi-ddc";
> >>>> +            bias-disable;
> >>>> +    };
> >>>> +
> >>>> +    /* switch to PF25 as gpio driving DDC_SDA low */
> >>>> +    pins_hdmi_ddc_unwedge: hdmi_ddc {
> >>>> +            function = "hdmi-ddc";
> >>>> +            groups = "hdmi-ddc";
> >>>> +            bias-disable;
> >>>> +    };
> >>>
> >>> Your pins_hdmi_ddc and pins_hdmi_ddc_unwedge are the exact same? You could just use the former and pass it to both pinctrl-0 and pinctrl-1.
> >>
> >> This was forgotten to remove. We do not make use of the unwedge feature because I could not find out how to use pinctrl to switch this to gpio25 and drive it low.
> >
> > Using gpio-hog?
>
> well, AFAIR it activates the gpio permanently and is a propery of the gpio controller and not of pinmux.

Yes, hogs are permanently (ignoring DT overlay tricks).

> The driver assumes it can use pinmux state switching to drive the DDC_SDA line low on demand.

Add an optional wedge-gpios property for switching?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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