Re: [PATCH 2/2] drm/amd/display: fix BT.2020 YCbCr output CSC matrices for DCE

[Nathan Lucas]

Hi Igor,

Thank you for taking the time to test the patches.  Your RX 580 should hit
the new limited-range matrix in dce_transform.c which I was not able to
directly test.

Thanks again,
Nathan

On Mon, Aug 3, 2026 at 9:25 AM Igor Paunovic <royalnet026@xxxxxxxxx> wrote:
>
> Hi Nathan,
>
> I hit exactly this on a DCE 11.2 part, so here is a data point for the
> path you could not test.
>
> Setup: XFX RX 580 8GB (Polaris10, DCE 11.2) as an external GPU on an
> Orange Pi 5 Plus (RK3588, arm64) over PCIe Gen3 x4, driving a Sony 65"
> HDR10 TV at 3840x2160@60 with HDR enabled under KWin/Wayland. The sink
> lists 3840x2160@60 only in its YCbCr 4:2:0 video data block and caps
> TMDS at 300 MHz, so the stream comes out as PIXEL_ENCODING_YCBCR420
> (confirmed in hardware: FMT_CONTROL = 0x002a0000, FMT_PIXEL_ENCODING = 2),
> and with the compositor setting Colorspace=BT2020_RGB the output color
> space ends up COLOR_SPACE_2020_YCBCR_LIMITED.
>
> My tree predates 51e6668ab4ba, so global_color_matrix[] had no BT.2020
> row at all. That is worth recording as its own failure mode: with no
> matching entry, dce110_opp_set_csc_default() programs no matrix and
> configure_graphics_mode() leaves OUTPUT_CSC_GRPH_MODE at 0, so the
> output CSC stays bypassed and plain RGB is fed to the 4:2:0 formatter
> while the AVI infoframe declares YCbCr 4:2:0 with BT.2020 colorimetry.
> The sink then applies a BT.2020 YCbCr to RGB matrix to RGB data: luma
> lands on green, Cb/Cr sit near mid scale, and the picture is washed out
> with a heavy green cast. SDR on the same link was fine, since it stays
> on the BT.709 entry.
>
> Applying 51e6668ab4ba plus this series on top of 7.0 fixes it: colors
> are correct on that TV in HDR, across a reboot, with no amdgpu errors in
> the log. As a cross-check, the same desktop on a second monitor driven
> by a completely different pipeline (the SoC's own display controller)
> now matches it.
>
> I also booted 51e6668ab4ba without this series on the same setup and
> could not tell the two apart by eye. That is not a counter-argument to
> the fix, just a note on sensitivity: the compositor maps SDR content to
> around 350 nits, so nothing gets near the top of the PQ range where the
> full-range luma scaling would clip, and the residual difference stays
> below what this TV's processing reveals.
>
> Tested-by: Igor Paunovic <royalnet026@xxxxxxxxx>
>
> Thanks,
> Igor