drm/i915: Get PM ref before accessing HW register

Seeing these errors when GT is likely in suspend state-
"RPM wakelock ref not held during HW access"

Ensure GT is awake before trying to access HW registers. Avoid
reading the register if that is not the case.
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Fixes: 41e5c17e ("drm/i915/guc/slpc: Sysfs hooks for SLPC")
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210907232704.12982-1-vinay.belgaumkar@intel.com

drivers/gpu/drm/i915/gt/intel_rps.c

@@ -1969,8 +1969,14 @@ u32 intel_rps_read_actual_frequency(struct intel_rps *rps)
 u32 intel_rps_read_punit_req(struct intel_rps *rps)
 {
 	struct intel_uncore *uncore = rps_to_uncore(rps);
+	struct intel_runtime_pm *rpm = rps_to_uncore(rps)->rpm;
+	intel_wakeref_t wakeref;
+	u32 freq = 0;
 
-	return intel_uncore_read(uncore, GEN6_RPNSWREQ);
+	with_intel_runtime_pm_if_in_use(rpm, wakeref)
+		freq = intel_uncore_read(uncore, GEN6_RPNSWREQ);
+
+	return freq;
 }
 
 static u32 intel_rps_get_req(u32 pureq)