[PATCH] drm: disable deep color when EDID violates spec

Alex Deucher alexdeucher at gmail.com
Tue Jan 10 19:54:19 UTC 2017


On Tue, Jan 10, 2017 at 12:46 PM, Ville Syrjälä
<ville.syrjala at linux.intel.com> wrote:
> On Tue, Jan 10, 2017 at 12:27:45PM -0500, Alex Deucher wrote:
>> On Tue, Jan 10, 2017 at 6:33 AM, Ernst Sjöstrand <ernstp at gmail.com> wrote:
>> > Isn't 10bpc very common among monitors, and 12bpc very rare? Or maybe I'm
>> > confusing the transport layer with the presentation capabilities...?
>> > Here are 201 monitors that claim 10bpc:
>> > http://pricespy.co.uk/category.php?l=s300859434&o=eg_401#prodlista
>> >
>>
>> FWIW, I've almost never seen a monitor that supports 12 bpc, but I've
>> see quite a few 10 bpc monitors.
>
> I've seen plenty of monitors that do 10bpc over DP, but I've never seen
> anything that does 10bpc over HDMI. 12bpc over HDMI is pretty common
> in "proper" TVs in my experience.
>
>> I can talk to our display team to
>> see what other OSes do.
>
> Thanks. That should give us some idea if anyone ever tried 10bpc
> over HDMI on these things.

We apparently see this pretty commonly, especially with freesync
monitors, and we support it.  It seems to be pretty prevalent because
you can support a higher refresh rate with a lower bpc.

Alex

>
>>
>> Alex
>>
>> > Regards
>> > //Ernst
>> >
>> > 2017-01-10 11:52 GMT+01:00 Ville Syrjälä <ville.syrjala at linux.intel.com>:
>> >>
>> >> On Thu, Jan 05, 2017 at 05:45:23PM -0600, Nicholas Sielicki wrote:
>> >> > As per the HDMI 1.3 and 1.4 spec, "deep color modes" are color depths
>> >> > greater than 24 bits per pixel. The spec explicitly states, "All Deep
>> >> > Color modes are optional though if an HDMI Source or Sink supports any
>> >> > Deep Color mode, it shall support 36-bit mode." (6.2.4 Color Depth
>> >> > Requirements).
>> >> >
>> >> > I came across a monitor (Acer X233H) that supplies an illegal EDID where
>> >> > DC_30bit is set and DC_36bit is not set. The end result is badly garbled
>> >> > output because the driver is sending 36BPP when the monitor can't handle
>> >> > it.
>> >> >
>> >> > Much of the intel hardware is incapable of operating at any
>> >> > bit-per-component setting outside of 8 or 12, and the spec seems to
>> >> > imply that if any deep color support is found, then it is a safe
>> >> > assumption to operate at 12.
>> >> >
>> >> > This patch ensures that the EDID is within the spec (specifically, that
>> >> > DC_36bit is set) before committing to going forward with any deep
>> >> > colors.  There was already a check for this EDID inconsistency, but it
>> >> > resulted only in a warning and did not fall-back to safer settings.
>> >> >
>> >> > CC: Ville Syrjälä <ville.syrjala at linux.intel.com>
>> >> > Signed-off-by: Nicholas Sielicki <nicholas.sielicki at gmail.com>
>> >> > ---
>> >> >  drivers/gpu/drm/drm_edid.c | 35 +++++++++++++++++++++++------------
>> >> >  1 file changed, 23 insertions(+), 12 deletions(-)
>> >> >
>> >> > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
>> >> > index 336be31ff3de..42ce3f54d2dc 100644
>> >> > --- a/drivers/gpu/drm/drm_edid.c
>> >> > +++ b/drivers/gpu/drm/drm_edid.c
>> >> > @@ -3772,30 +3772,34 @@ static void
>> >> > drm_parse_hdmi_deep_color_info(struct drm_connector *connector,
>> >> >  {
>> >> >       struct drm_display_info *info = &connector->display_info;
>> >> >       unsigned int dc_bpc = 0;
>> >> > +     u8 modes = 0;
>> >> >
>> >> >       /* HDMI supports at least 8 bpc */
>> >> >       info->bpc = 8;
>> >> >
>> >> > +     /* Ensure all DC modes are unset if we return early */
>> >> > +     info->edid_hdmi_dc_modes = 0;
>> >>
>> >> Clearing this in drm_add_display_info() should be sufficient since
>> >> this guy doesn't get called from anywhere else. So this part could
>> >> be droppped.
>> >>
>> >> Otherwise this feels like a decent way to handle the problem. We
>> >> could of course try to use the 10bpc (or whatever) deep color modes
>> >> the sink claims to support, but given that the people designing the
>> >> thing didn't bother reading the spec, it seems safer to just disable
>> >> deep color support entirely.
>> >>
>> >> Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
>> >>
>> >> > +
>> >> >       if (cea_db_payload_len(hdmi) < 6)
>> >> >               return;
>> >> >
>> >> >       if (hdmi[6] & DRM_EDID_HDMI_DC_30) {
>> >> >               dc_bpc = 10;
>> >> > -             info->edid_hdmi_dc_modes |= DRM_EDID_HDMI_DC_30;
>> >> > +             modes |= DRM_EDID_HDMI_DC_30;
>> >> >               DRM_DEBUG("%s: HDMI sink does deep color 30.\n",
>> >> >                         connector->name);
>> >> >       }
>> >> >
>> >> >       if (hdmi[6] & DRM_EDID_HDMI_DC_36) {
>> >> >               dc_bpc = 12;
>> >> > -             info->edid_hdmi_dc_modes |= DRM_EDID_HDMI_DC_36;
>> >> > +             modes |= DRM_EDID_HDMI_DC_36;
>> >> >               DRM_DEBUG("%s: HDMI sink does deep color 36.\n",
>  >> >                         connector->name);
>> >> >       }
>> >> >
>> >> >       if (hdmi[6] & DRM_EDID_HDMI_DC_48) {
>> >> >               dc_bpc = 16;
>> >> > -             info->edid_hdmi_dc_modes |= DRM_EDID_HDMI_DC_48;
>> >> > +             modes |= DRM_EDID_HDMI_DC_48;
>> >> >               DRM_DEBUG("%s: HDMI sink does deep color 48.\n",
>> >> >                         connector->name);
>> >> >       }
>> >> > @@ -3806,9 +3810,24 @@ static void drm_parse_hdmi_deep_color_info(struct
>> >> > drm_connector *connector,
>> >> >               return;
>> >> >       }
>> >> >
>> >> > +     /*
>> >> > +      * All deep color modes are optional, but if a sink supports any
>> >> > deep
>> >> > +      * color mode, it must support 36-bit mode. If this is found not
>> >> > +      * to be the case, sink is in violation of HDMI 1.3 / 1.4 spec and
>> >> > it
>> >> > +      * is prudent to disable all deep color modes. Return here before
>> >> > +      * committing bpc and edid_hdmi_dc_modes.
>> >> > +      */
>> >> > +     if (!(modes & DRM_EDID_HDMI_DC_36)) {
>> >> > +             DRM_DEBUG("%s: HDMI sink should do DC_36, but does
>> >> > not!\n",
>> >> > +                       connector->name);
>> >> > +             return;
>> >> > +     }
>> >> > +
>> >> > +
>> >> >       DRM_DEBUG("%s: Assigning HDMI sink color depth as %d bpc.\n",
>> >> >                 connector->name, dc_bpc);
>> >> >       info->bpc = dc_bpc;
>> >> > +     info->edid_hdmi_dc_modes = modes;
>> >> >
>> >> >       /*
>> >> >        * Deep color support mandates RGB444 support for all video
>> >> > @@ -3823,15 +3842,6 @@ static void drm_parse_hdmi_deep_color_info(struct
>> >> > drm_connector *connector,
>> >> >               DRM_DEBUG("%s: HDMI sink does YCRCB444 in deep color.\n",
>> >> >                         connector->name);
>> >> >       }
>> >> > -
>> >> > -     /*
>> >> > -      * Spec says that if any deep color mode is supported at all,
>> >> > -      * then deep color 36 bit must be supported.
>> >> > -      */
>> >> > -     if (!(hdmi[6] & DRM_EDID_HDMI_DC_36)) {
>> >> > -             DRM_DEBUG("%s: HDMI sink should do DC_36, but does
>> >> > not!\n",
>> >> > -                       connector->name);
>> >> > -     }
>> >> >  }
>> >> >
>> >> >  static void
>> >> > @@ -3895,6 +3905,7 @@ static void drm_add_display_info(struct
>> >> > drm_connector *connector,
>> >> >       /* driver figures it out in this case */
>> >> >       info->bpc = 0;
>> >> >       info->color_formats = 0;
>> >> > +     info->edid_hdmi_dc_modes = 0;
>> >> >       info->cea_rev = 0;
>> >> >       info->max_tmds_clock = 0;
>> >> >       info->dvi_dual = false;
>> >> > --
>> >> > 2.11.0
>> >>
>> >> --
>> >> Ville Syrjälä
>> >> Intel OTC
>> >> _______________________________________________
>> >> dri-devel mailing list
>> >> dri-devel at lists.freedesktop.org
>> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>> >
>> >
>> >
>> > _______________________________________________
>> > dri-devel mailing list
>> > dri-devel at lists.freedesktop.org
>> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>> >
>
> --
> Ville Syrjälä
> Intel OTC


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