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

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Message-Id: <DD6EFFDC-EB04-4C39-8A63-3825C3A9C64D@goldelico.com>
Date:   Thu, 25 Nov 2021 09:29:02 +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 Gert,

> Am 25.11.2021 um 08:58 schrieb Geert Uytterhoeven <geert@...ux-m68k.org>:
> 
> Hi Nikolaus,
> 
> On Wed, Nov 24, 2021 at 5:31 PM H. Nikolaus Schaller <hns@...delico.com> wrote:
>>> Am 24.11.2021 um 17:21 schrieb Geert Uytterhoeven <geert@...ux-m68k.org>:
>>> 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.
> 
> 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?

That would touch the synopsys driver core and does not appear to be required for jz4780 operation.
We just add a separate driver specialisation for some parameters and set up the device tree.

So it is beyond the scope of our work (neither needed, nor can we test it).
If you want to add that, please go ahead.

BR and thanks,
Nikolaus