Re: [PATCH 03/11] drm: parse ycbcr 420 vdb block

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, May 08, 2017 at 10:11:53PM +0530, Sharma, Shashank wrote:
> Regards
> 
> Shashank
> 
> 
> On 5/8/2017 9:54 PM, Ville Syrjälä wrote:
> > On Fri, Apr 07, 2017 at 07:39:20PM +0300, Shashank Sharma wrote:
> >> From: Jose Abreu <jose.abreu@synopsys.com>
> >>
> >> HDMI 2.0 spec adds support for ycbcr420 subsampled output.
> >> CEA-861-F adds two new blocks in EDID, to provide information about
> >> sink's support for ycbcr420 output.
> >>
> >> These new blocks are:
> >> - ycbcr420 video data (vdb) block: video modes which can be supported
> >>    only in ycbcr420 output mode.
> >> - ycbcr420 video capability data (vcb) block: video modes which can be
> >>    support in ycbcr420 output mode also (along with RGB, YCBCR 444/422 etc)
> >>
> >> This patch adds parsing and handling of ycbcr420-vdb in the DRM
> >> layer.
> >>
> >> This patch is a modified version of Jose's RFC patch:
> >> https://patchwork.kernel.org/patch/9492327/
> >> so the authorship is maintained.
> >>
> >> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> >> Signed-off-by: Jose Abreu <joabreu@synopsys.com>
> >> Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
> >> ---
> >>   drivers/gpu/drm/drm_edid.c  | 54 +++++++++++++++++++++++++++++++++++++++++++--
> >>   drivers/gpu/drm/drm_modes.c | 10 +++++++--
> >>   include/drm/drm_connector.h |  1 +
> >>   include/uapi/drm/drm_mode.h |  6 +++++
> >>   4 files changed, 67 insertions(+), 4 deletions(-)
> > <snip>
> >> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> >> index 4eeda12..cef76b2 100644
> >> --- a/include/drm/drm_connector.h
> >> +++ b/include/drm/drm_connector.h
> >> @@ -199,6 +199,7 @@ struct drm_display_info {
> >>   #define DRM_COLOR_FORMAT_RGB444		(1<<0)
> >>   #define DRM_COLOR_FORMAT_YCRCB444	(1<<1)
> >>   #define DRM_COLOR_FORMAT_YCRCB422	(1<<2)
> >> +#define DRM_COLOR_FORMAT_YCRCB420	(1<<2)
> >>   
> >>   	/**
> >>   	 * @color_formats: HDMI Color formats, selects between RGB and YCrCb
> >> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> >> index 8c67fc0..1e74d8e 100644
> >> --- a/include/uapi/drm/drm_mode.h
> >> +++ b/include/uapi/drm/drm_mode.h
> >> @@ -84,6 +84,12 @@ extern "C" {
> >>   #define  DRM_MODE_FLAG_3D_L_DEPTH_GFX_GFX_DEPTH	(6<<14)
> >>   #define  DRM_MODE_FLAG_3D_TOP_AND_BOTTOM	(7<<14)
> >>   #define  DRM_MODE_FLAG_3D_SIDE_BY_SIDE_HALF	(8<<14)
> >> +/*
> >> + * HDMI 2.0
> >> + */
> >> +#define DRM_MODE_FLAG_420_MASK			(0x03<<23)
> >> +#define  DRM_MODE_FLAG_420			(1<<23)
> >> +#define  DRM_MODE_FLAG_420_ONLY			(1<<24)
> > Adding those would again break the uabi. We can't add new mode flags
> > without some kind of client cap.
> > But I think we agreed that new user
> > space visible mode flags aren't needed, and instad we can keep it all
> > internal?
> Yep you are right, we had decided to keep it internal, and this whole 
> patch series is implemented in such a way only, to control everything 
> through the HDMI output property itself.
> But may be I slightly misunderstood that we shouldn't add the flags bits 
> all together, and I added this flag to differentiate between YCBCR420 
> and notmal modes.
> Can you please suggest me on:
> - how to differentiate a YCBCR420 mode with normal mode ? I still need 
> to add a flag, but not expose it into uapi layer.

I guess we can just tack on a few new bools to the end of
drm_display_mode. And then when we get the mode passed in by the user
we'll have to check whether that mode matches any CEA mode and
then look up the correct YCbCr 4:2:0 mode for it.

Hmm. Actually, that probably means that it isn't sufficient to
actually store this information on the modes we have on the connector's
mode list, because that list has been filtered and so may not actually
have all the modes that were declared in the EDID. So I'm thinking we
should perhaps make the bitmap parsed from the Y402CMDB index the
full CEA mode list. That we can just lookup the matching VIC for
the user provided mode and check whether the bit for that VIC
indicates 4:2:0 support. And maybe we can handle Y420VDB in exactly
the same way (ie. just a second bitmap). That would have the additional
nice feature that the maximum length of those bitmaps is well defined
(at most 256 VICs).

-- 
Ville Syrjälä
Intel OTC
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