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

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Message-ID: <20191128083940.GC10251@fsr-ub1664-121>
Date:   Thu, 28 Nov 2019 08:39:41 +0000
From:   Laurentiu Palcu <laurentiu.palcu@....com>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
CC:     Uma Shankar <uma.shankar@...el.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [EXT] Re: [PATCH] drm: fix HDR static metadata type field
 numbering

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@....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