[Bug 206347] New: amdgpu.dc=1 breaks power management on RX480

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=206347

            Bug ID: 206347
           Summary: amdgpu.dc=1 breaks power management on RX480
           Product: Drivers
           Version: 2.5
    Kernel Version: 5.4.14
          Hardware: x86-64
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri at kernel-bugs.osdl.org
          Reporter: matare at fh-aachen.de
        Regression: No

I've been using an AMD RX480 with amdgpu ever since it was supported (i.e.
since ~4.8 I think). Somehow I almost got used to the fact that, when idling,
it uses 15-20 Watt more than in Windows. Recently I investigated again and
found that it simply never reduces the GPU clock below 1278Mhz.

I found this related bug report on freedesktop.org:
https://gitlab.freedesktop.org/drm/amd/issues/817

And this comment on Phoronix...
https://www.phoronix.com/forums/forum/linux-graphics-x-org-drivers/open-source-amd-linux/1046724-rx-580-idles-at-1300mhz-core-clock?p=1047617#post1047617

... which gave the crucial hint of setting amdgpu.dc=0

It is only with this setting that my GPU clock will be reduced to 300 MHz on
idle as it should. My system runs perfectly fine, performance is good, and
system idle power consumption is down to ~70W from the ~90W I had before. So I
don't understand why we're wasting 20W by default on all those chips. Maybe
there is something that should be fixed or it should default to off?

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