drm/i915: sanitize rps irq disabling

When disabling the RPS interrupts there is a tricky dependency between
the thread disabling the interrupts, the RPS interrupt handler and the
corresponding RPS work. The RPS work can reenable the interrupts, so
there is no straightforward order in the disabling thread to (1) make
sure that any RPS work is flushed and to (2) disable all RPS
interrupts. Currently this is solved by masking the interrupts using two
separate mask registers (first level display IMR and PM IMR) and doing
the disabling when all first level interrupts are disabled.

This works, but the requirement to run with all first level interrupts
disabled is unnecessary making the suspend / unload time ordering of RPS
disabling wrt. other unitialization steps difficult and error prone.
Removing this restriction allows us to disable RPS early during suspend
/ unload and forget about it for the rest of the sequence. By adding a
more explicit method for avoiding the above race, it also becomes easier
to prove its correctness. Finally currently we can hit the WARN in
snb_update_pm_irq(), when a final RPS work runs with the first level
interrupts already disabled. This won't lead to any problem (due to the
separate interrupt masks), but with the change in this and the next
patch we can get rid of the WARN, while leaving it in place for other
scenarios.

To address the above points, add a new RPS interrupts_enabled flag and
use this during RPS disabling to avoid requeuing the RPS work and
reenabling of the RPS interrupts. Since the interrupt disabling happens
now in intel_suspend_gt_powersave(), we will disable RPS interrupts
explicitly during suspend (and not just through the first level mask),
but there is no problem doing so, it's also more consistent and allows
us to unify more of the RPS disabling during suspend and unload time in
the next patch.

v2/v3:
- rebase on patch "drm/i915: move rps irq disable one level up" in the
  patchset
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -998,8 +998,12 @@ struct intel_rps_ei {
 };
 
 struct intel_gen6_power_mgmt {
-	/* work and pm_iir are protected by dev_priv->irq_lock */
+	/*
+	 * work, interrupts_enabled and pm_iir are protected by
+	 * dev_priv->irq_lock
+	 */
 	struct work_struct work;
+	bool interrupts_enabled;
 	u32 pm_iir;
 
 	/* Frequencies are stored in potentially platform dependent multiples.

drivers/gpu/drm/i915/i915_irq.c

@@ -274,6 +274,7 @@ void gen6_enable_rps_interrupts(struct drm_device *dev)
 	spin_lock_irq(&dev_priv->irq_lock);
 	WARN_ON(dev_priv->rps.pm_iir);
 	WARN_ON(I915_READ(gen6_pm_iir(dev_priv)) & dev_priv->pm_rps_events);
+	dev_priv->rps.interrupts_enabled = true;
 	gen6_enable_pm_irq(dev_priv, dev_priv->pm_rps_events);
 	spin_unlock_irq(&dev_priv->irq_lock);
 }
@@ -282,14 +283,16 @@ void gen6_disable_rps_interrupts(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
+	spin_lock_irq(&dev_priv->irq_lock);
+	dev_priv->rps.interrupts_enabled = false;
+	spin_unlock_irq(&dev_priv->irq_lock);
+
+	cancel_work_sync(&dev_priv->rps.work);
+
 	I915_WRITE(GEN6_PMINTRMSK, INTEL_INFO(dev_priv)->gen >= 8 ?
 		   ~GEN8_PMINTR_REDIRECT_TO_NON_DISP : ~0);
 	I915_WRITE(gen6_pm_ier(dev_priv), I915_READ(gen6_pm_ier(dev_priv)) &
 				~dev_priv->pm_rps_events);
-	/* Complete PM interrupt masking here doesn't race with the rps work
-	 * item again unmasking PM interrupts because that is using a different
-	 * register (PMIMR) to mask PM interrupts. The only risk is in leaving
-	 * stale bits in PMIIR and PMIMR which gen6_enable_rps will clean up. */
 
 	spin_lock_irq(&dev_priv->irq_lock);
 	dev_priv->rps.pm_iir = 0;
@@ -1135,6 +1138,11 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	int new_delay, adj;
 
 	spin_lock_irq(&dev_priv->irq_lock);
+	/* Speed up work cancelation during disabling rps interrupts. */
+	if (!dev_priv->rps.interrupts_enabled) {
+		spin_unlock_irq(&dev_priv->irq_lock);
+		return;
+	}
 	pm_iir = dev_priv->rps.pm_iir;
 	dev_priv->rps.pm_iir = 0;
 	/* Make sure not to corrupt PMIMR state used by ringbuffer on GEN6 */
@@ -1708,11 +1716,12 @@ static void gen6_rps_irq_handler(struct drm_i915_private *dev_priv, u32 pm_iir)
 
 	if (pm_iir & dev_priv->pm_rps_events) {
 		spin_lock(&dev_priv->irq_lock);
-		dev_priv->rps.pm_iir |= pm_iir & dev_priv->pm_rps_events;
 		gen6_disable_pm_irq(dev_priv, pm_iir & dev_priv->pm_rps_events);
+		if (dev_priv->rps.interrupts_enabled) {
+			dev_priv->rps.pm_iir |= pm_iir & dev_priv->pm_rps_events;
+			queue_work(dev_priv->wq, &dev_priv->rps.work);
+		}
 		spin_unlock(&dev_priv->irq_lock);
-
-		queue_work(dev_priv->wq, &dev_priv->rps.work);
 	}
 
 	if (INTEL_INFO(dev_priv)->gen >= 8)

drivers/gpu/drm/i915/intel_pm.c

@@ -6186,9 +6186,17 @@ void intel_suspend_gt_powersave(struct drm_device *dev)
 	/* Interrupts should be disabled already to avoid re-arming. */
 	WARN_ON(intel_irqs_enabled(dev_priv));
 
+	if (INTEL_INFO(dev)->gen < 6)
+		return;
+
 	flush_delayed_work(&dev_priv->rps.delayed_resume_work);
 
-	cancel_work_sync(&dev_priv->rps.work);
+	/*
+	 * TODO: disable RPS interrupts on GEN9+ too once RPS support
+	 * is added for it.
+	 */
+	if (INTEL_INFO(dev)->gen < 9)
+		gen6_disable_rps_interrupts(dev);
 
 	/* Force GPU to min freq during suspend */
 	gen6_rps_idle(dev_priv);
@@ -6217,13 +6225,6 @@ void intel_disable_gt_powersave(struct drm_device *dev)
 		else
 			gen6_disable_rps(dev);
 
-		/*
-		 * TODO: disable RPS interrupts on GEN9+ too once RPS support
-		 * is added for it.
-		 */
-		if (INTEL_INFO(dev)->gen < 9)
-			gen6_disable_rps_interrupts(dev);
-
 		dev_priv->rps.enabled = false;
 		mutex_unlock(&dev_priv->rps.hw_lock);
 	}