[PATCH 1/3] drm/i915/pmu: Disable on PREEMPT_RT

[Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>]

From: Maarten Lankhorst <dev@lankhorst.se>

I tried to come up with alternative and lockless approaches
to make pmu work, but since the perf events are run in
atomic context on PREEMPT_RT, ordinary spinlocks no longer
work and forcewake and register accesses become problematic.

Disable perf events on PREEMPT_RT for now, without affecting
!PREEMPT_RT users.

Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>
---
v2: s/reeturn/return/
---
 drivers/gpu/drm/i915/i915_pmu.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index 1c3bafda9c70..9ea5626399e5 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -1156,6 +1156,16 @@ void i915_pmu_register(struct drm_i915_private *i915)
 	};
 	int ret = -ENOMEM;
 
+	/*
+	 * PREEMPT_RT has problems with forcewake. Forcewake is used by the
+	 * engine 'busy' event when guc submission is enabled, and to measure
+	 * rc6 residency.
+	 *
+	 * Disable pmu events on PREEMPT_RT entirely to prevent deadlocks.
+	 */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT))
+		return;
+
 	spin_lock_init(&pmu->lock);
 	hrtimer_setup(&pmu->timer, i915_sample, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	init_rc6(pmu);
-- 
2.55.0