[Bug 102468] RX470 powerplay issues on hybrid laptop system (dGPU does not power down)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102468

            Bug ID: 102468
           Summary: RX470 powerplay issues on hybrid laptop system (dGPU
                    does not power down)
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: taijian at posteo.de

Created attachment 133866
  --> https://bugs.freedesktop.org/attachment.cgi?id=133866&action=edit
relevant dmesg output

I have an Alienware 15R3 laptop with hybrid Intel (HD 630) / AMD (RX470)
graphics. I run Arch Linux, up to date as of 2017-08-29.

My issue is that when booting the laptop with a 'normal' kernel command line,
the dGPU *never* turns off, even when it is not normally needed in desktop
operations. This is confirmed by running powertop, which reports a power drain
of ~36 W even under basically zero load. This is accompanied by various
[powerplay] error messages in dmesg. As a side effect, the CPU is blocked from
going to power states below pc2.

If I blacklist amdgpu in the kcl and then force the dGPU to off with acpi_call,
the reported power consumption in powertop drops to ~12 W, with a corresponding
increase in battery time. The CPU is now able to reach pc3.

Booting into Windows 10 also gives me the same battery time as blacklisting
amdgpu in Linux, but also the expected 'on-demand-switching' of the dGPU that I
expect from such a setup. This is just to confirm that this is not a hardware
issue - it is definitely possible to dynamically switch the dGPU on or off from
the OS level, the implementation is just botched in amdgpu.

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