linux-kernel - Re: [PATCH v8 6/8] MIPS: DTS: CI20: Add DT nodes for HDMI setup

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Message-Id: <B622D2B5-D631-43F3-9D50-2B41681C78AB@goldelico.com>
Date:   Wed, 24 Nov 2021 17:30:05 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Paul Cercueil <paul@...pouillou.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Harry Wentland <harry.wentland@....com>,
        Sam Ravnborg <sam@...nborg.org>,
        Maxime Ripard <maxime@...no.tech>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Paul Boddie <paul@...die.org.uk>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        letux-kernel@...nphoenux.org, Jonas Karlman <jonas@...boo.se>,
        DRI Development <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v8 6/8] MIPS: DTS: CI20: Add DT nodes for HDMI setup

Hi Geert,

> Am 24.11.2021 um 17:21 schrieb Geert Uytterhoeven <geert@...ux-m68k.org>:
> 
> Hi Nikolaus,
> 
> On Wed, Nov 24, 2021 at 5:19 PM H. Nikolaus Schaller <hns@...delico.com> wrote:
>>> Am 23.11.2021 um 21:10 schrieb Paul Cercueil <paul@...pouillou.net>:
>>> Le mar., nov. 23 2021 at 19:13:59 +0100, H. Nikolaus Schaller <hns@...delico.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.
The driver assumes it can use pinmux state switching to drive the DDC_SDA line low on demand.

Since it is unlikely that we need it at all (and we have no test case that it works) I think we simply can leave
this driver feature unused unless we get a test case.

BR and thanks,
Nikolaus