drm/i915/pmu: Don't grab wakeref when enabling events

Chris found a CI report which points out calling intel_runtime_pm_get from
inside i915_pmu_enable hook is not allowed since it can be invoked from
hard irq context. This is something we knew but forgot, so lets fix it
once again.

We do this by syncing the internal book keeping with hardware rc6 counter
on driver load.

v2:
 * Always sync on parking and fully sync on init.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: f4e9894b ("drm/i915/pmu: Correct the rc6 offset upon enabling")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20201214094349.3563876-1-tvrtko.ursulin@linux.intel.com

drivers/gpu/drm/i915/i915_pmu.c

@@ -103,11 +103,6 @@ static unsigned int event_bit(struct perf_event *event)
 	return config_bit(event->attr.config);
 }
 
-static bool event_read_needs_wakeref(const struct perf_event *event)
-{
-	return event->attr.config == I915_PMU_RC6_RESIDENCY;
-}
-
 static bool pmu_needs_timer(struct i915_pmu *pmu, bool gpu_active)
 {
 	struct drm_i915_private *i915 = container_of(pmu, typeof(*i915), pmu);
@@ -213,13 +208,24 @@ static u64 get_rc6(struct intel_gt *gt)
 	return val;
 }
 
-static void park_rc6(struct drm_i915_private *i915)
+static void init_rc6(struct i915_pmu *pmu)
 {
-	struct i915_pmu *pmu = &i915->pmu;
+	struct drm_i915_private *i915 = container_of(pmu, typeof(*i915), pmu);
+	intel_wakeref_t wakeref;
 
-	if (pmu->enable & config_mask(I915_PMU_RC6_RESIDENCY))
+	with_intel_runtime_pm(i915->gt.uncore->rpm, wakeref) {
 		pmu->sample[__I915_SAMPLE_RC6].cur = __get_rc6(&i915->gt);
+		pmu->sample[__I915_SAMPLE_RC6_LAST_REPORTED].cur =
+					pmu->sample[__I915_SAMPLE_RC6].cur;
+		pmu->sleep_last = ktime_get();
+	}
+}
 
+static void park_rc6(struct drm_i915_private *i915)
+{
+	struct i915_pmu *pmu = &i915->pmu;
+
+	pmu->sample[__I915_SAMPLE_RC6].cur = __get_rc6(&i915->gt);
 	pmu->sleep_last = ktime_get();
 }
 
@@ -230,6 +236,7 @@ static u64 get_rc6(struct intel_gt *gt)
 	return __get_rc6(gt);
 }
 
+static void init_rc6(struct i915_pmu *pmu) { }
 static void park_rc6(struct drm_i915_private *i915) {}
 
 #endif
@@ -655,15 +662,10 @@ static void i915_pmu_enable(struct perf_event *event)
 {
 	struct drm_i915_private *i915 =
 		container_of(event->pmu, typeof(*i915), pmu.base);
-	bool need_wakeref = event_read_needs_wakeref(event);
 	struct i915_pmu *pmu = &i915->pmu;
-	intel_wakeref_t wakeref = 0;
 	unsigned long flags;
 	unsigned int bit;
 
-	if (need_wakeref)
-		wakeref = intel_runtime_pm_get(&i915->runtime_pm);
-
 	bit = event_bit(event);
 	if (bit == -1)
 		goto update;
@@ -678,13 +680,6 @@ static void i915_pmu_enable(struct perf_event *event)
 	GEM_BUG_ON(bit >= ARRAY_SIZE(pmu->enable_count));
 	GEM_BUG_ON(pmu->enable_count[bit] == ~0);
 
-	if (pmu->enable_count[bit] == 0 &&
-	    config_mask(I915_PMU_RC6_RESIDENCY) & BIT_ULL(bit)) {
-		pmu->sample[__I915_SAMPLE_RC6_LAST_REPORTED].cur = 0;
-		pmu->sample[__I915_SAMPLE_RC6].cur = __get_rc6(&i915->gt);
-		pmu->sleep_last = ktime_get();
-	}
-
 	pmu->enable |= BIT_ULL(bit);
 	pmu->enable_count[bit]++;
 
@@ -726,9 +721,6 @@ static void i915_pmu_enable(struct perf_event *event)
 	 * an existing non-zero value.
 	 */
 	local64_set(&event->hw.prev_count, __i915_pmu_event_read(event));
-
-	if (wakeref)
-		intel_runtime_pm_put(&i915->runtime_pm, wakeref);
 }
 
 static void i915_pmu_disable(struct perf_event *event)
@@ -1187,6 +1179,7 @@ void i915_pmu_register(struct drm_i915_private *i915)
 	hrtimer_init(&pmu->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	pmu->timer.function = i915_sample;
 	pmu->cpuhp.cpu = -1;
+	init_rc6(pmu);
 
 	if (!is_igp(i915)) {
 		pmu->name = kasprintf(GFP_KERNEL,