[Bug 99250] [SKL,IVB] HDMI and DP: EDID-supplied BPP is not always properly clamped.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99250

Nicholas Sielicki <sielicki at yandex.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |WONTFIX

--- Comment #2 from Nicholas Sielicki <sielicki at yandex.com> ---
HDMI 1.3A spec says the following

> 6.2.4 Color Depth Requirements
> 
> HDMI Sources and Sinks may support color depths of 24, 30, 36 and/or 48 bits
> per pixel. All HDMI Sources and Sinks shall support 24 bits per pixel.  Color
> depths greater than 24 bits are defined to be “Deep Color” modes. All Deep
> Color modes are optional though if an HDMI Source or Sink supports any Deep
> Color mode, it shall support 36-bit mode.
> 
> For each supported Deep Color mode, RGB 4:4:4 shall be supported and optionally
> YCBCR 4:4:4 may be supported.
> 
> YCBCR 4:2:2 is not permitted for any Deep Color mode.
> 
> An HDMI Sink shall support all EDID-indicated Deep Color modes on all
> EDID-indicated video formats except if that combination exceeds the
> Max_TMDS_Clock indication.
> 
> An HDMI Source shall not send any Deep Color mode to a Sink that does not
> indicate support for that mode.

The take away: it is illegal for DC_30bit to be set without DC_36bit also being
set.

The EDID claims the following:

> CEA extension block
> Extension version: 3
> 30 bytes of CEA data
>  <...>
>  Vendor-specific data block, OUI 000c03 (HDMI)
>    Source physical address 1.0.0.0
>    DC_30bit

Note the lack of DC_36bit.

While i915 is technically sending DC_36bit (a deep color mode) to a sink that
does not indicate support for that mode, the monitor clearly violated the spec
first and in a worse way. Had the monitor not violated the spec, i915 would not
have violated the spec.

So I think this can be chalked up as a bad monitor operating outside the spec.

I'm going to close this bug.                                                    

(Thank you to everyone on #intel-gfx for the help.)

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