drm/i915/icl: Deal with GT INT DW correctly

BSpec says:

"Second level interrupt events are stored in the GT INT DW. GT INT DW is
a double buffered structure. A snapshot of events is taken when SW reads
GT INT DW. From the time of read to the time of SW completely clearing
GT INT DW (to indicate end of service), all incoming interrupts are logged
in a secondary storage structure. this guarantees that the record of
interrupts SW is servicing will not change while under service".

We read GT INT DW in several places now:

- The IRQ handler (banks 0 and 1) where, hopefully, it is completely
  cleared (operation now covered with the irq lock).
- The 'reset' interrupts functions for RPS and GuC logs, where we clear
  the bit we are interested in and leave the others for the normal
  interrupt handler.
- The 'enable' interrupts functions for RPS and GuC logs, as a measure
  of precaution. Here we could relax a bit and don't check GT INT DW
  at all or, if we do, at least we should clear the offending bit
  (which is what this patch does).

Note that, if every bit is cleared on reading GT INT DW, the register
won't be locked. Also note that, according to the BSpec, GT INT DW
cannot be cleared without first servicing the Selector & Shared IIR
registers.

v2:
  - Remove some code duplication (Tvrtko)
  - Make sure GT_INTR_DW are protected by the irq spinlock, since it's a
    global resource (Tvrtko)

v3: Optimize the spinlock (Tvrtko)

v4: Rebase.
v5:
  - take spinlock on outer scope to please sparse (Mika)
  - use raw_reg accessors (Mika)
v6: omit the continue in looping banks (Michel)

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> (v4)
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180406093237.14548-1-mika.kuoppala@linux.intel.com

drivers/gpu/drm/i915/i915_irq.c

@@ -243,6 +243,41 @@ void i915_hotplug_interrupt_update(struct drm_i915_private *dev_priv,
 	spin_unlock_irq(&dev_priv->irq_lock);
 }
 
+static u32
+gen11_gt_engine_identity(struct drm_i915_private * const i915,
+			 const unsigned int bank, const unsigned int bit);
+
+static bool gen11_reset_one_iir(struct drm_i915_private * const i915,
+				const unsigned int bank,
+				const unsigned int bit)
+{
+	void __iomem * const regs = i915->regs;
+	u32 dw;
+
+	lockdep_assert_held(&i915->irq_lock);
+
+	dw = raw_reg_read(regs, GEN11_GT_INTR_DW(bank));
+	if (dw & BIT(bit)) {
+		/*
+		 * According to the BSpec, DW_IIR bits cannot be cleared without
+		 * first servicing the Selector & Shared IIR registers.
+		 */
+		gen11_gt_engine_identity(i915, bank, bit);
+
+		/*
+		 * We locked GT INT DW by reading it. If we want to (try
+		 * to) recover from this succesfully, we need to clear
+		 * our bit, otherwise we are locking the register for
+		 * everybody.
+		 */
+		raw_reg_write(regs, GEN11_GT_INTR_DW(bank), BIT(bit));
+
+		return true;
+	}
+
+	return false;
+}
+
 /**
  * ilk_update_display_irq - update DEIMR
  * @dev_priv: driver private
@@ -412,26 +447,12 @@ static void gen6_disable_pm_irq(struct drm_i915_private *dev_priv, u32 disable_m
 	/* though a barrier is missing here, but don't really need a one */
 }
 
-static u32
-gen11_gt_engine_identity(struct drm_i915_private * const i915,
-			 const unsigned int bank, const unsigned int bit);
-
 void gen11_reset_rps_interrupts(struct drm_i915_private *dev_priv)
 {
-	u32 dw;
-
 	spin_lock_irq(&dev_priv->irq_lock);
 
-	/*
-	 * According to the BSpec, DW_IIR bits cannot be cleared without
-	 * first servicing the Selector & Shared IIR registers.
-	 */
-	dw = I915_READ_FW(GEN11_GT_INTR_DW0);
-	while (dw & BIT(GEN11_GTPM)) {
-		gen11_gt_engine_identity(dev_priv, 0, GEN11_GTPM);
-		I915_WRITE_FW(GEN11_GT_INTR_DW0, BIT(GEN11_GTPM));
-		dw = I915_READ_FW(GEN11_GT_INTR_DW0);
-	}
+	while (gen11_reset_one_iir(dev_priv, 0, GEN11_GTPM))
+		;
 
 	dev_priv->gt_pm.rps.pm_iir = 0;
 
@@ -455,10 +476,12 @@ void gen6_enable_rps_interrupts(struct drm_i915_private *dev_priv)
 
 	spin_lock_irq(&dev_priv->irq_lock);
 	WARN_ON_ONCE(rps->pm_iir);
+
 	if (INTEL_GEN(dev_priv) >= 11)
-		WARN_ON_ONCE(I915_READ_FW(GEN11_GT_INTR_DW0) & BIT(GEN11_GTPM));
+		WARN_ON_ONCE(gen11_reset_one_iir(dev_priv, 0, GEN11_GTPM));
 	else
 		WARN_ON_ONCE(I915_READ(gen6_pm_iir(dev_priv)) & dev_priv->pm_rps_events);
+
 	rps->interrupts_enabled = true;
 	gen6_enable_pm_irq(dev_priv, dev_priv->pm_rps_events);
 
@@ -2778,6 +2801,8 @@ gen11_gt_engine_identity(struct drm_i915_private * const i915,
 	u32 timeout_ts;
 	u32 ident;
 
+	lockdep_assert_held(&i915->irq_lock);
+
 	raw_reg_write(regs, GEN11_IIR_REG_SELECTOR(bank), BIT(bit));
 
 	/*
@@ -2853,36 +2878,47 @@ gen11_gt_identity_handler(struct drm_i915_private * const i915,
 }
 
 static void
-gen11_gt_irq_handler(struct drm_i915_private * const i915,
-		     const u32 master_ctl)
+gen11_gt_bank_handler(struct drm_i915_private * const i915,
+		      const unsigned int bank)
 {
 	void __iomem * const regs = i915->regs;
-	unsigned int bank;
+	unsigned long intr_dw;
+	unsigned int bit;
 
-	for (bank = 0; bank < 2; bank++) {
-		unsigned long intr_dw;
-		unsigned int bit;
+	lockdep_assert_held(&i915->irq_lock);
 
-		if (!(master_ctl & GEN11_GT_DW_IRQ(bank)))
-			continue;
+	intr_dw = raw_reg_read(regs, GEN11_GT_INTR_DW(bank));
 
-		intr_dw = raw_reg_read(regs, GEN11_GT_INTR_DW(bank));
+	if (unlikely(!intr_dw)) {
+		DRM_ERROR("GT_INTR_DW%u blank!\n", bank);
+		return;
+	}
 
-		if (unlikely(!intr_dw)) {
-			DRM_ERROR("GT_INTR_DW%u blank!\n", bank);
-			continue;
-		}
+	for_each_set_bit(bit, &intr_dw, 32) {
+		const u32 ident = gen11_gt_engine_identity(i915,
+							   bank, bit);
 
-		for_each_set_bit(bit, &intr_dw, 32) {
-			const u32 ident = gen11_gt_engine_identity(i915,
-								   bank, bit);
+		gen11_gt_identity_handler(i915, ident);
+	}
 
-			gen11_gt_identity_handler(i915, ident);
-		}
+	/* Clear must be after shared has been served for engine */
+	raw_reg_write(regs, GEN11_GT_INTR_DW(bank), intr_dw);
+}
 
-		/* Clear must be after shared has been served for engine */
-		raw_reg_write(regs, GEN11_GT_INTR_DW(bank), intr_dw);
+static void
+gen11_gt_irq_handler(struct drm_i915_private * const i915,
+		     const u32 master_ctl)
+{
+	unsigned int bank;
+
+	spin_lock(&i915->irq_lock);
+
+	for (bank = 0; bank < 2; bank++) {
+		if (master_ctl & GEN11_GT_DW_IRQ(bank))
+			gen11_gt_bank_handler(i915, bank);
 	}
+
+	spin_unlock(&i915->irq_lock);
 }
 
 static irqreturn_t gen11_irq_handler(int irq, void *arg)