linux-kernel - Re: [PATCH v2 4/4] drm/panel-edp: Add some panels with conservative timings

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Message-ID: <CAD=FV=U6M5rpQXmjC+iGf0BGtiyjRAAcMfo4Fr3pDyYVp3m4aQ@mail.gmail.com>
Date:   Thu, 7 Dec 2023 10:23:53 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Pin-yen Lin <treapking@...omium.org>
Cc:     Neil Armstrong <neil.armstrong@...aro.org>,
        Jessica Zhang <quic_jesszhan@...cinc.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org,
        Guenter Roeck <groeck@...omium.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 4/4] drm/panel-edp: Add some panels with conservative timings

Hi,

On Thu, Dec 7, 2023 at 12:18 AM Pin-yen Lin <treapking@...omium.org> wrote:
>
> These panels are used by Mediatek MT8173 Chromebooks but we can't find
> the corresponding data sheets, and these panels used to work on v4.19
> kernel without any specified delays.
>
> Therefore, instead of having them use the default conservative timings,
> update them with less-conservative timings from other panels of the same
> vendor. The panels should still work under those timings, and we can
> save some delays and suppress the warnings.
>
> Signed-off-by: Pin-yen Lin <treapking@...omium.org>
>
> ---
>
> (no changes since v1)
>
>  drivers/gpu/drm/panel/panel-edp.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)

Reviewed-by: Douglas Anderson <dianders@...omium.org>

Repeating my comments from v1 here too, since I expect this patch to
sit on the lists for a little while:

This is OK w/ me, but it will need time on the mailing lists before
landing in case anyone else has opinions. Specifical thoughts:

* I at least feel fairly confident that this is OK since these panels
essentially booted without _any_ delays back on the old downstream
v4.19 kernel. Presumably the panels just had fairly robust timing
controllers and so worked OK, but it's better to get the timing more
correct.

* This is definitely better than the very conservative timings and the
WARN_ON splat.

* I don't love the "Unknown" string, but it doesn't do anything other
than print to dmesg anyway and at least it conveys to anyone else
reading the table that the timings may not be quite as tight.