DSC always used, even if unnecessary

The issue is that DSC is always used, even if unnecessary, when DP has enough bandwidth. Measured by reading /sys/kernel/debug/dri/0/DP-1/dsc_clock_en, and switching the display modes.

• 4k@144Hz: DSC correctly used
• 4k@120Hz: DSC still used
• 4k@96Hz: DSC still used (even though DP 1.4 has enough bandwidth to do this at 10 bits with no compression)
• 4k@60Hz: DSC not used

All tests were done at 8 bits per pixel.

• GPU: 6900XT
• Display(s): Acer Technologies XV282K KV 11221B8C44200
• Type of Display Connection: DP
• Distro name and Version: Debian Unstable
• Kernel version: 5.19-rc1
• Custom kernel: Torvalds' repo

Another user (Nefsen402) was also able to replicate this on a 27GN950 monitor on a stock 5.18 kernel, so it's not a recent regression. I tested and could replicate it on 5.17.

changed the description

added DC label

Ping? DSC can be very noticeable, depending on bitrate, making it not very useful for graphics or multimedia work.

Also seeing this, 6900XT and ASUS PG43U.

I can disable DSC on my monitor and if I do so the resolutions up to and including 4k 98Hz work without it, as expected.

mentioned in issue #2446

Ping

added feature-request label

I think given that DSC gives noticeable compression artifacts and is often buggy (giving even more artifacts), it's a little more than a feature request.

Absolutely this is a bug and not a feature request. DSC makes every image purple for me and enabling it when it is not required is contrary to the behaviour on any other platform.

ping