[Intel-gfx] [PATCH] drm/i915: Stop sampling rc6 from inside pmu_enable

[Chris Wilson]

Quoting Chris Wilson (2020-12-03 22:38:49)
> Since rc6 is sampling the device registers, we try to acquire the device
> wakeref. However, since i915_pmu_enable may be called from hardirq, we
> cannot actually wake the device up. So let's not, and hope our gt wake
> tracking is accurate.

    drm/i915/pmu: Correct the rc6 offset upon enabling

    The rc6 residency starts ticking from 0 from BIOS POST, but the kernel
    starts measuring the time from its boot. If we start measuruing
    I915_PMU_RC6_RESIDENCY while the GT is idle, we start our sampling from
    0 and then upon first activity (park/unpark) add in all the rc6
    residency since boot. After the first park with the sampler engaged, the
    sleep/active counters are aligned.

    v2: With a wakeref to be sure

    Closes: https://gitlab.freedesktop.org/drm/intel/issues/973

Hmm. Take 2.
-Chris