[Bug 96645] New: Low package c-states used only after forcing DPSM to off

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96645

            Bug ID: 96645
           Summary: Low package c-states used only after forcing DPSM to
                    off
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: gabriele.mzt at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

I noticed that with v4.7-rc4 the CPU of my laptop can only enter package
c-state 2, while it can normally enter pc7 with v4.6 or older kernels.

I also noticed that after I turned the screen off once running 'xset dpms force
off', the CPU can enter pc7, no matter what's the current state of the display.

I ran a bisection and found that the regression was introduced with commit
ed4a6a7ca853253f9b86f3005d76345482a71283 ("drm/i915: Add two-stage ILK-style
watermark programming (v11)").

My laptop has an i7-4500U CPU and its integrated HD Graphics 4400.

I'm not sure what kind of information are needed to debug the problem, so let
me know what other information I should provide.

Thanks,
Gabriele

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