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

Laurentiu Palcu
2019-11-28T08:39:47Z

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.

Thanks,
laurentiu

>
> >
> > Signed-off-by: Laurentiu Palcu <laurentiu.palcu@nxp.com>
> > ---
> > include/linux/hdmi.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/hdmi.h b/include/linux/hdmi.h
> > index 9918a6c..216e25e 100644
> > --- a/include/linux/hdmi.h
> > +++ b/include/linux/hdmi.h
> > @@ -155,7 +155,7 @@ enum hdmi_content_type {
> > };
> >
> > enum hdmi_metadata_type {
> > - HDMI_STATIC_METADATA_TYPE1 = 1,
> > + HDMI_STATIC_METADATA_TYPE1 = 0,
> > };
> >
> > enum hdmi_eotf {
> > --
> > 2.7.4
>
> --
> Ville Syrjälä
> Intel