[PATCH 2/7] drm/edid: Allow to ignore the audio EDID data

[Alex Deucher]

On Mon, Mar 4, 2019 at 2:53 PM Eric Anholt <eric at anholt.net> wrote:
>
> Maxime Ripard <maxime.ripard at bootlin.com> writes:
>
> > In some cases, in order to accomodate with displays with poor EDIDs, we
> > need to ignore that the monitor alledgedly supports audio output and
> > disable the audio output.
> >
> > Signed-off-by: Maxime Ripard <maxime.ripard at bootlin.com>
> > ---
> >  drivers/gpu/drm/drm_edid.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> > index 990b1909f9d7..c0258b011bb2 100644
> > --- a/drivers/gpu/drm/drm_edid.c
> > +++ b/drivers/gpu/drm/drm_edid.c
> > @@ -4190,6 +4190,11 @@ bool drm_detect_hdmi_monitor(struct edid *edid)
> >  }
> >  EXPORT_SYMBOL(drm_detect_hdmi_monitor);
> >
> > +static bool ignore_edid_audio = false;
> > +module_param(ignore_edid_audio, bool, 0644);
> > +MODULE_PARM_DESC(ignore_edid_audio,
> > +              "Ignore the EDID and always consider that a monitor doesn't have audio capabilities");
> > +
> >  /**
> >   * drm_detect_monitor_audio - check monitor audio capability
> >   * @edid: EDID block to scan
> > @@ -4209,6 +4214,9 @@ bool drm_detect_monitor_audio(struct edid *edid)
> >       bool has_audio = false;
> >       int start_offset, end_offset;
> >
> > +     if (ignore_edid_audio)
> > +             goto end;
> > +
> >       edid_ext = drm_find_cea_extension(edid);
> >       if (!edid_ext)
> >               goto end;
>
> It looks like the motivation for the original flag on Raspberry Pi was
> "I've got a non-audio monitor, but the system comes up trying to play
> audio to HDMI instead of the analog jack".  Do we have some way for DRM
> to communicate to ALSA that this is not the right place to try to play
> audio by default?

Apparently not.  We have users using debug knobs in our drivers to
disable display audio because ALSA defaults to that rather than other
audio.

Alex