Re: [EXT] Re: [PATCH] drm: fix HDR static metadata type field numbering

[Ville Syrjälä]

On Thu, Nov 28, 2019 at 08:39:41AM +0000, Laurentiu Palcu wrote:
> On Wed, Nov 27, 2019 at 05:17:03PM +0200, Ville Syrjälä wrote:
> > Caution: EXT Email
> > 
> > On Wed, Nov 27, 2019 at 02:42:35PM +0000, Laurentiu Palcu wrote:
> > > According to CTA-861 specification, HDR static metadata data block allows a
> > > sink to indicate which HDR metadata types it supports by setting the SM_0 to
> > > SM_7 bits. Currently, only Static Metadata Type 1 is supported and this is
> > > indicated by setting the SM_0 bit to 1.
> > >
> > > However, the connector->hdr_sink_metadata.hdmi_type1.metadata_type is always
> > > 0, because hdr_metadata_type() in drm_edid.c checks the wrong bit.
> > >
> > > This patch corrects the HDMI_STATIC_METADATA_TYPE1 bit position.
> > 
> > Was confused for a while why this has even been workning, but I guess
> > that's due to userspace populating the metadata infoframe blob correctly
> > even if we misreported the metadata types in the parsed EDID metadata
> > blob.
> > 
> > Hmm. Actually on further inspection this all seems to be dead code. The
> > only thing we seem to use from the parsed EDID metadata stuff is
> > eotf bitmask. We check that in drm_hdmi_infoframe_set_hdr_metadata()
> > but we don't check the metadata type.
> > 
> > Maybe we should just nuke this EDID parsing stuff entirely? Seems
> > pretty much pointless.
> 
> I've been thinking about that but we may need the rest of the fields as
> well, even though they're not currently used. I'm referring to sink's
> min/max luminance data. Shouldn't we also check min/max cll, besides
> eotf, to make sure the source does not pass higher/lower luminance
> values, than the sink supports, for optimal content rendering?
> 
> However, CTA-861 is not very clear on how a sink should behave if
> the CLL values exceed the allowed range... :/ Also, if the CLL range or
> the FALL values passed in the DRM infoframe exceed the sink's advertised
> min/max values, I guess the sink cannot go lower/higher than it can
> anyway. In which case, we don't really need the rest of the HDR static
> metadata block and nuking that part should be ok.

I'm thinking we should just conclude that such userspace is a 
buggy mess and deserves whatever it gets.

-- 
Ville Syrjälä
Intel