Tonga Kernel Modesetting Issue

[Ian Bashford]

Hi,
I'm investigating an issue with KMS on my graphics card. I'm hoping this
list might give me some direction/guidance where to look.

Sometime in between kernels 4.9 and 4.14, the KMS on my card stopped
getting set to 2560x1440 and only sets 1920x1080.  Passing video= as a
kernel parameter just leads to a black screen.
I've tried stock kernels on alpine and arch, and also compiled a few as
well; I can't see any obvious differences in the compile options that might
lead to the difference.
My next line of enquiry is to see if there's a change in amdgpu that might
be the cause.
Given the size of the codebase and the number of changes, I was hoping
someone might be able to help me narrow the possible search.

Would you be able to suggest somewhere to begin ?

The card is a Sapphire R9 380X NITRO 4GB  - it identifies as a TONGA.

During the boot, I get this message about the mode setting
[drm] initializing kernel modesetting (TONGA 0x1002:0x6938 0x174B:0xE308
0xF1)

thanks
Ian
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