[Intel-gfx] DP compliance failure due to dithering for 18bpp video pattern

[Manasi Navare]

Hi All,

We are seeing CRC check failures in some of the 18bpp video pattern
DP Compliance tests causing the tests to fail. On further investigation, it is
rootcaused to dithering that the i915 driver enables in case of 18bpp pipe
configuration that messes up the CRC and causes the test to fail.

Some of the approaches that can solve this problem are:
1.  Add a new method in intel_dp.c to request the compliance test state.
Call this new method in intel_display.c to not enable dithering during a
compliance test. Issue with this is it makes the general portion of the driver
compliance aware.

2.  Move the dithering enable to compute_config methods in all encoder source
files. Issue: Lot of duplicate code and DP is the only encoder that uses 18bpc.

3.  Disable dithering at all times in the driver. However this can cause image
quality issue with 8bpc plane and 6 bit pipe.

Any suggestions on which approach can be implemented in order to pass
compliance?

Regards
Manasi