linux-kernel - Re: [RFC PATCH] drm/edid: drm_add_modes_noedid() should set lowest resolution as preferred

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Date:   Fri, 06 May 2022 14:16:22 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Doug Anderson <dianders@...omium.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Sankeerth Billakanti <quic_sbillaka@...cinc.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] drm/edid: drm_add_modes_noedid() should set lowest
 resolution as preferred

On Thu, 05 May 2022, Doug Anderson <dianders@...omium.org> wrote:
> Ville,
>
> On Tue, Apr 26, 2022 at 1:21 PM Douglas Anderson <dianders@...omium.org> wrote:
>>
>> If we're unable to read the EDID for a display because it's corrupt /
>> bogus / invalid then we'll add a set of standard modes for the
>> display. When userspace looks at these modes it doesn't really have a
>> good concept for which mode to pick and it'll likely pick the highest
>> resolution one by default. That's probably not ideal because the modes
>> were purely guesses on the part of the Linux kernel.
>>
>> Let's instead set 640x480 as the "preferred" mode when we have no EDID.
>>
>> Signed-off-by: Douglas Anderson <dianders@...omium.org>
>> ---
>>
>>  drivers/gpu/drm/drm_edid.c | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>
> Someone suggested that you might have an opinion on this patch and
> another one I posted recently [1]. Do you have any thoughts on it?
> Just to be clear: I'm hoping to land _both_ this patch and [1]. If you
> don't have an opinion, that's OK too.
>
> [1] https://lore.kernel.org/r/20220426114627.2.I4ac7f55aa446699f8c200a23c10463256f6f439f@changeid

There are a number of drivers with combos:

	drm_add_modes_noedid()
	drm_set_preferred_mode()

which I think would be affected by the change. Perhaps you should just
call drm_set_preferred_mode() in your referenced patch?

Alternatively, perhaps drm_set_preferred_mode() should erase the
previous preferred mode(s) if it finds a matching new preferred mode.


BR,
Jani.

-- 
Jani Nikula, Intel Open Source Graphics Center