Half FPS with Visionox VTDR6130 in DSC and CMD mode on SM8550

When adding patch https://lore.kernel.org/all/20230728012623.22991-1-quic_parellan@quicinc.com/ on top of v6.5-rc5 which adds DSC and CMD mode to the Visionox VTDR6130 panel present on the SM8550 MTP & QRD, when using modetetxt vsync test, I get half the FPS:

# modetest -r -v
<snip>
setting mode 1080x2400-144.00Hz on connectors 32, crtc 95
failed to set gamma: Function not implemented
freq: 74.22Hz
freq: 73.09Hz
freq: 72.48Hz 

Instead of 144Hz when in Video mode without the patch.