[Intel-gfx] [RFC v5 0/6] drm/i915/dp: Preliminary support for DP YCbCr4:2:0 outputs

[Gwan-gyeong Mun]

On Gen 11 platform, to enable resolutions like 5K at 120 (or higher) we need
to use DSC (DP 1.4) or YCbCr4:2:0 (DP 1.3 or 1.4) on DP.
In order to support YCbCr4:2:0 on DP we need to program YCBCR 4:2:0
to MSA and VSC SDP.

This patches are RFC patches that add a VSC structure for handling
Pixel Encoding/Colorimetry Formats and program YCBCR 4:2:0 to MSA and VSC SDP.

This is currently not tested, but I wanted to get some inputs on this approach.
The idea of a scaling (RGB -> YCbCr4:4:4 -> YCbCr 4:2:0) is to follow the
same approach used in YCbCr 4:2:0 on HDMI.

v2: Addressed Maarten's review comments, fixed minor coding and block comment
style. And reordered a first patch  ("drm/i915/dp: Support DP ports
YUV 4:2:0 output to GEN11") as a last patch.

v3: Addressed Ville's review comments.
Style fixed with few naming.
If lscon is active, it makes not to call intel_dp_ycbcr420_config() to avoid
to clobber of lspcon_ycbcr420_config() routine.
And it move the 420_only check into the intel_dp_ycbcr420_config().
Remove a changing of pipe_bpp on intel_ddi_set_pipe_settings().
Because the pipe is running at the full bpp, keep pipe_bpp as RGB even though
YCbCr 4:2:0 output format is used.
Add a link bandwidth computation for YCbCr4:2:0 output format.

v4: Fix uninitialized return value which is reported by Dan Carpenter.

v5: Addressed reivew comments from Ville.
In order to make codes simple, it adds and uses intel_dp_output_bpp() function.
In order to avoid the extra indentation, it inverts if-clause on
intel_dp_ycbcr420_config().
Remove the error print where no errors print are allowed.

Gwan-gyeong Mun (6):
  drm/i915/dp: Add a config function for YCBCR420 outputs
  drm: Add a VSC structure for handling Pixel Encoding/Colorimetry
    Formats
  drm/i915/dp: Program VSC Header and DB for Pixel Encoding/Colorimetry
    Format
  drm/i915/dp: Add a support of YCBCR 4:2:0 to DP MSA
  drm/i915/dp: Change a link bandwidth computation for DP YCbCr 4:2:0
    output
  drm/i915/dp: Support DP ports YUV 4:2:0 output to GEN11

 drivers/gpu/drm/i915/i915_reg.h  |   1 +
 drivers/gpu/drm/i915/intel_ddi.c |   9 ++
 drivers/gpu/drm/i915/intel_dp.c  | 156 ++++++++++++++++++++++++++++++-
 drivers/gpu/drm/i915/intel_drv.h |   2 +
 include/drm/drm_dp_helper.h      |  17 ++++
 5 files changed, 180 insertions(+), 5 deletions(-)

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2.21.0