drm/i915: mask RPS IRQs properly when disabling RPS

Atm, igt/gem_reset_stats can trigger the recently added WARN on
left-over PM_IIR bits in gen6_enable_rps_interrupts(). There are two
reasons for this:
1. we call intel_enable_gt_powersave() without a preceeding
   intel_disable_gt_powersave()
2. gen6_disable_rps_interrupts() doesn't mask interrupts in PM_IMR

1. means RPS interrupts will remain enabled and can be serviced during
the HW initialization after a GPU reset. 2. means even if we called
gen6_disable_rps_interrupts() any new RPS interrupt during RPS
initialization would still propagate to PM_IIR too early (though
wouldn't be serviced).

This patch solves the 2. issue by also masking interrupts in PM_IMR, the
following patch fixes 1. getting rid of the WARN. This also makes
intel_enable_gt_powersave() and intel_disable_gt_powersave() more
symmetric.

Since gen6_disable_rps_interrupts() is called during driver loading with
i915 interrupts disabled add a new version of gen6_disable_pm_irq() that
doesn't WARN for this.

Also while at it, get the irq_lock around the whole PM_IMR/IER/IIR
programming sequence and make sure that any queued PM_IIR bit is also
cleared.

The WARN was caught by PRTS after I sent my previous RPS sanitizing
patchset and I could easily reproduce it on HSW. To actually fix it we
also need the next patch.
Reported-by: He, Shuang <shuang.he@intel.com>
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_irq.c

@@ -231,9 +231,6 @@ static void snb_update_pm_irq(struct drm_i915_private *dev_priv,
 
 	assert_spin_locked(&dev_priv->irq_lock);
 
-	if (WARN_ON(!intel_irqs_enabled(dev_priv)))
-		return;
-
 	new_val = dev_priv->pm_irq_mask;
 	new_val &= ~interrupt_mask;
 	new_val |= (~enabled_irq_mask & interrupt_mask);
@@ -247,14 +244,26 @@ static void snb_update_pm_irq(struct drm_i915_private *dev_priv,
 
 void gen6_enable_pm_irq(struct drm_i915_private *dev_priv, uint32_t mask)
 {
+	if (WARN_ON(!intel_irqs_enabled(dev_priv)))
+		return;
+
 	snb_update_pm_irq(dev_priv, mask, mask);
 }
 
-void gen6_disable_pm_irq(struct drm_i915_private *dev_priv, uint32_t mask)
+static void __gen6_disable_pm_irq(struct drm_i915_private *dev_priv,
+				  uint32_t mask)
 {
 	snb_update_pm_irq(dev_priv, mask, 0);
 }
 
+void gen6_disable_pm_irq(struct drm_i915_private *dev_priv, uint32_t mask)
+{
+	if (WARN_ON(!intel_irqs_enabled(dev_priv)))
+		return;
+
+	__gen6_disable_pm_irq(dev_priv, mask);
+}
+
 void gen6_reset_rps_interrupts(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -289,16 +298,20 @@ void gen6_disable_rps_interrupts(struct drm_device *dev)
 
 	cancel_work_sync(&dev_priv->rps.work);
 
+	spin_lock_irq(&dev_priv->irq_lock);
+
 	I915_WRITE(GEN6_PMINTRMSK, INTEL_INFO(dev_priv)->gen >= 8 ?
 		   ~GEN8_PMINTR_REDIRECT_TO_NON_DISP : ~0);
+
+	__gen6_disable_pm_irq(dev_priv, dev_priv->pm_rps_events);
 	I915_WRITE(gen6_pm_ier(dev_priv), I915_READ(gen6_pm_ier(dev_priv)) &
 				~dev_priv->pm_rps_events);
+	I915_WRITE(gen6_pm_iir(dev_priv), dev_priv->pm_rps_events);
+	I915_WRITE(gen6_pm_iir(dev_priv), dev_priv->pm_rps_events);
 
-	spin_lock_irq(&dev_priv->irq_lock);
 	dev_priv->rps.pm_iir = 0;
-	spin_unlock_irq(&dev_priv->irq_lock);
 
-	I915_WRITE(gen6_pm_iir(dev_priv), dev_priv->pm_rps_events);
+	spin_unlock_irq(&dev_priv->irq_lock);
 }
 
 /**