linux-kernel - Re: [PATCH v2 1/3] drm_edid: Support getting EDID through ddc without connector

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Date: Wed, 28 Feb 2024 16:54:37 -0800
From: Hsin-Yi Wang <hsinyi@...omium.org>
To: Doug Anderson <dianders@...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>, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] drm_edid: Support getting EDID through ddc without connector

On Wed, Feb 28, 2024 at 4:21 PM Doug Anderson <dianders@...omium.org> wrote:
>
> Hi,
>
> On Tue, Feb 27, 2024 at 5:11 PM Hsin-Yi Wang <hsinyi@...omium.org> wrote:
> >
> > Some panels are interested in the EDID during early probe when connector
> > is still unknown.
> >
> > Add a function drm_get_edid_no_connector() to get edid without connector.
> > No functional change for existing usage.
> >
> > Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> > ---
> > v1->v2:
> > add a function to return the entire edid without updating connector.
> > ---
> >  drivers/gpu/drm/drm_edid.c | 45 ++++++++++++++++++++++++++++----------
> >  include/drm/drm_edid.h     |  1 +
> >  2 files changed, 34 insertions(+), 12 deletions(-)
>
> I'll respond in the discussion in v1 too, but overall I'm not a fan of
> reading the whole EDID twice at bootup. Personally I'd love to see us
> to back to just reading the base block like in v1, but I guess we can
> see what Jani and others say.
>
>
> > @@ -2385,18 +2385,20 @@ static struct edid *_drm_do_get_edid(struct drm_connector *connector,
> >         if (status == EDID_BLOCK_READ_FAIL)
> >                 goto fail;
> >
> > -       /* FIXME: Clarify what a corrupt EDID actually means. */
> > -       if (status == EDID_BLOCK_OK || status == EDID_BLOCK_VERSION)
> > -               connector->edid_corrupt = false;
> > -       else
> > -               connector->edid_corrupt = true;
> > +       if (connector) {
> > +               /* FIXME: Clarify what a corrupt EDID actually means. */
> > +               if (status == EDID_BLOCK_OK || status == EDID_BLOCK_VERSION)
> > +                       connector->edid_corrupt = false;
> > +               else
> > +                       connector->edid_corrupt = true;
> >
> > -       if (!edid_block_status_valid(status, edid_block_tag(edid))) {
> > -               if (status == EDID_BLOCK_ZERO)
> > -                       connector->null_edid_counter++;
> > +               if (!edid_block_status_valid(status, edid_block_tag(edid))) {
> > +                       if (status == EDID_BLOCK_ZERO)
> > +                               connector->null_edid_counter++;
> >
> > -               connector_bad_edid(connector, edid, 1);
> > -               goto fail;
> > +                       connector_bad_edid(connector, edid, 1);
> > +                       goto fail;
>
> This "goto fail" is now only run "if (connector)" which means that
> you're not properly checking if the EDID is valid when "connector ==
> NULL", right? That seems like a bug unless I missed something...

We can't check with connector_bad_edid() since there's no connector.
But we still check with edid_block_read() status, similar to what the
original drm_edid_get_panel_id() checks.