Comment # 5 on bug 1177770 from Takashi Iwai

Back from side-step: the basic strategy to find the already existing fix is
"divide-and-conquer".  That is, we want to narrow down the possible ranges at
first.

For example, trying different kernel version and check whether the problem is
fixed -- that would be already a great help.  There are some old kernels
available in my OBS repos, e.g. OBS home:tiwai:kernel:5.4,
home:tiwai:kernel:5.5, etc.  Leap 15.2 is 5.3, and suppose you've tested 5.8.y
in Kernel:stable, then identify which version between them (5.4, 5.5, 5.6, 5.7)
starts working.

Once after you figure out the first working kernel, we want to see the kernel
debug messages from DRM stack.  Boot the kernel with drm.debug=0x0e option and
give the dmesg outputs from both working and non-working cases.  It allows us
to compare which modes are wrongly configured.

Ideally, after this, we may perform git bisection or such, but this would
require the manual kernel build, so it's not always a feasible option.