On Tue, Jan 10, 2017 at 03:39:42PM +0200, Jani Nikula wrote: > On Tue, 10 Jan 2017, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > 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. > >> > > I thought there was a related bugzilla? Where's the reference? Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99250 > > >> CC: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > >> Signed-off-by: Nicholas Sielicki <nicholas.sielicki@xxxxxxxxx> > >> --- > >> 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. > > Hmmh. > > So currently, the sink in question violates this, "All Deep Color modes > are optional though if an HDMI Source or Sink supports any Deep Color > mode, it shall support 36-bit mode." > > But also currently, we violate this, "An HDMI Source shall not send any > Deep Color mode to a Sink that does not indicate support for that mode." > > Instead of fixing our violation, this patch points fingers at the > violating sinks, and refuses to play ball with any deep colors. > > Just to get the record straight, is that a fair assesment? More or less. i915 can't violate the spec unless the sink violates the spec as well. I did actually write a patch once to explicitly check the DC_36 bit in i915 code, but I don't think I ever sent it out as I figured it's an impossible scenario. But I should have known better and assumed that some sink will eventually violate the spec. -- Ville Syrjälä Intel OTC _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
