My MSI r9 390 forces the memory clock to 150000 if I plug in more than one monitor. The card draws 40 watts more power while idle and keeps the fans running all the time. This is happening with both amdgpu and radeon and I can fix the problem by disabling dpm, but this causes some other issues. I read earlier that this behaviour is intended and is a common problem with graphics cards but IIRC a recent driver update fixed this on windows so I'd like to know if there is any chance to also get a fix on linux?
mclk changes have to be synced to the vertical blanking period of the displays. If the displays have different timings, it's not possible to change the mclk without causing display flickering.
So does the windows driver detect the timing of the displays and keep the mclk low if it's in sync?
AFAIK, the windows driver forces the mclk high as well when multiple displays are attached. The only possible exception would be if multiple displays had the exact same timing and the vblank periods could be aligned.
Yeah, both my monitors are the same model so this is probably the case. If there's no way to enable changing the mclk, can I set it to a lower default value without disabling dpm completely?
I have a similar problem. I have a Rx 580 with 2 exactly equal monitors. On windows, there is no issue and memory clock is always at 300mhz, except when gaming. When on linux, If using graphical display, memory clock is always MAX. If i am only on the tty's ( text mode only ) I can set it to 300mhz, after changing memory clock pp setting ( echo 1 > pp_mclk_od ). Like the op, drawing 40 watts more power than windows, is very undesirable, besides also running much cooler on windows. Also on windows I never saw any problem whatsoever with it running at minimum 300mhz.
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