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On suspend, the rc6 residency counters (stored in HW registers) will be lost and cleared. However, we keep track of the rc6 residency to provide a continuous 64b sampling, and if we see the HW value go backwards, we assume it overflowed and add on 32b/40b -- an interesting artifact when sampling across suspend. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200114105648.2172026-2-chris@chris-wilson.co.uk