For those using a DisplayPort to HDMI dongle currently with the AMDGPU Linux kernel graphics driver may find some higher resolutions / modes unavailable. Fortunately, a fix is on the way for dealing with this situation due to an oversight in the kernel driver.
It turns out the AMDGPU kernel driver has accidentally been limiting the clock to 165MHz even though HDMI 1.3+ bumped the clock to 340MHz. That in turn could cause issues for DP-HDMI dongles trying to run high resolution displays due to the bandwidth requirements being exceeded when bound to 165MHz.
As part of today’s batch of AMDGPU DC updates working their way to the Linux kernel, the AMDGPU driver will now properly bump the clock speed from 165MHz to 340MHz for capable outputs in order to allow those higher modes to be advertised and used:
[Why]
DP-HDMI dongles can execeed bandwidth requirements on high resolution monitors. This can lead to pruning the high resolution modes.HDMI 1.3 bumped the clock to 340MHz, but display code never matched it.
[How]
Set default to (DVI) 165MHz. Once HDMI display is identified update to 340MHz.
With the timing of the patch it will hopefully be picked up for the upcoming Linux 6.20~7.0 kernel cycle.
