linux-kernel - Re: [PATCH] drm: drm_probe_helper: add modes upto 1920x1080

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Date:   Tue, 16 Nov 2021 09:50:20 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     Angus Ainslie <angus@...ea.ca>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>, kernel@...i.sm,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm: drm_probe_helper: add modes upto 1920x1080

On Tue, Nov 16, 2021 at 9:44 AM Jani Nikula <jani.nikula@...ux.intel.com> wrote:
>
>
> Cc: Ville
>
> On Mon, 15 Nov 2021, Angus Ainslie <angus@...ea.ca> wrote:
> > Lots of monitors nowdays support more than 1024x768 so if the EDID is
> > unknown then add resolutions upto 1920x1080.
>
> IIUC it's supposed to be the fallback that's pretty much guaranteed to
> work. What's going to happen if we add 1920x1080 and it fails?

Yeah unless we are now in a times where monitors fail to light up
these very low resolutions then I don't think adding more here is a
good idea. This absolute fallback list is _not_ about making things
good, but about getting anything onto the screen. If we really, really
need this (and then it needs good reasons) then a defensive approach
might be to add more modes, but still leave the old 1024x768 as the
preferred one. That would avoid any regression potential.

Otherwise this just becomes a game of "I want to have the best mode
for my broken screen without working edid as the default", which is
no-go.
-Daniel

> BR,
> Jani.
>
> >
> > Signed-off-by: Angus Ainslie <angus@...ea.ca>
> > ---
> >  drivers/gpu/drm/drm_probe_helper.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> > index e7e1ee2aa352..5ad66ae9916e 100644
> > --- a/drivers/gpu/drm/drm_probe_helper.c
> > +++ b/drivers/gpu/drm/drm_probe_helper.c
> > @@ -517,7 +517,7 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
> >
> >       if (count == 0 && (connector->status == connector_status_connected ||
> >                          connector->status == connector_status_unknown))
> > -             count = drm_add_modes_noedid(connector, 1024, 768);
> > +             count = drm_add_modes_noedid(connector, 1920, 1080);
> >       count += drm_helper_probe_add_cmdline_mode(connector);
> >       if (count == 0)
> >               goto prune;
>
> --
> Jani Nikula, Intel Open Source Graphics Center



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch