meson: Enabling full-range HDMI output

[neil.armstrong at linaro.org]

Hi,

On 23/10/2024 10:00, Francisco Ayala Le Brun wrote:
> Hello,
> 
> I am seeking some guidance regarding enabling full-range HDMI output.
> Specifically, I am wondering which component in the video pipeline
> could be clamping HDMI output values to 16-235? Further details
> follow:
> 
> I have been trying to get full-range HDMI output from a Le Potato
> s905x SBC. At the moment, HDMI output seems to be hard-coded to color
> quantization limited range (16-235). This greatly diminishes the
> contrast in full range displays.
> 
> So far setting the VIU_OSD1/2_FULL_RANGE bit in the
> VIU_OSD1/2_CTRL_STAT2 register does not seem to work. I have also
> looked at the color space conversion matrix in dw_hdmi in case that is
> the culprit, but the values seem fine and setting that to zero does
> produce a signal in the full range (0). The buffer from the VIU is
> using a YUV format so dw_hdmi is not using the full to limited range
> conversion matrix.

Indeed the internal VPU pipeline is in 10bit YUV444, so it requires enabling
the dw-hdmi CSC, so perhaps those are not designed to output full-range RGB ?

Could you revert:
d3d6b1bf85ae drm: bridge: dw_hdmi: fix preference of RGB modes over YUV420

This would give you direct YUV444 HDMI output without CSC involved, reverting
is not an options because of low-cost HDMI panels lying in their EDID
and not really supporting YUV HDMI...

So if the original YUV is in full range, the culprit is in the DW-HDMI CSC
table.

Neil

> 
> Thank you in advance,
> Francisco
> 
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