drm/i915: Reduce locking in execlist command submission

This eliminates six needless spin lock/unlock pairs when writing out
ELSP.

v2: Respin with my preferred colour.
v3: Mostly back to the original colour

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> [v1]
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -2537,6 +2537,13 @@ void intel_uncore_forcewake_get(struct drm_i915_private *dev_priv,
 				enum forcewake_domains domains);
 void intel_uncore_forcewake_put(struct drm_i915_private *dev_priv,
 				enum forcewake_domains domains);
+/* Like above but the caller must manage the uncore.lock itself.
+ * Must be used with I915_READ_FW and friends.
+ */
+void intel_uncore_forcewake_get__locked(struct drm_i915_private *dev_priv,
+					enum forcewake_domains domains);
+void intel_uncore_forcewake_put__locked(struct drm_i915_private *dev_priv,
+					enum forcewake_domains domains);
 void assert_forcewakes_inactive(struct drm_i915_private *dev_priv);
 static inline bool intel_vgpu_active(struct drm_device *dev)
 {
@@ -3229,6 +3236,17 @@ int intel_freq_opcode(struct drm_i915_private *dev_priv, int val);
 #define POSTING_READ(reg)	(void)I915_READ_NOTRACE(reg)
 #define POSTING_READ16(reg)	(void)I915_READ16_NOTRACE(reg)
 
+/* These are untraced mmio-accessors that are only valid to be used inside
+ * criticial sections inside IRQ handlers where forcewake is explicitly
+ * controlled.
+ * Think twice, and think again, before using these.
+ * Note: Should only be used between intel_uncore_forcewake_irqlock() and
+ * intel_uncore_forcewake_irqunlock().
+ */
+#define I915_READ_FW(reg__) readl(dev_priv->regs + (reg__))
+#define I915_WRITE_FW(reg__, val__) writel(val__, dev_priv->regs + (reg__))
+#define POSTING_READ_FW(reg__) (void)I915_READ_FW(reg__)
+
 /* "Broadcast RGB" property */
 #define INTEL_BROADCAST_RGB_AUTO 0
 #define INTEL_BROADCAST_RGB_FULL 1

drivers/gpu/drm/i915/intel_lrc.c

@@ -315,17 +315,19 @@ static void execlists_elsp_write(struct intel_engine_cs *ring,
 	desc[3] = (u32)(temp >> 32);
 	desc[2] = (u32)temp;
 
-	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);
-	I915_WRITE(RING_ELSP(ring), desc[1]);
-	I915_WRITE(RING_ELSP(ring), desc[0]);
-	I915_WRITE(RING_ELSP(ring), desc[3]);
+	spin_lock(&dev_priv->uncore.lock);
+	intel_uncore_forcewake_get__locked(dev_priv, FORCEWAKE_ALL);
+	I915_WRITE_FW(RING_ELSP(ring), desc[1]);
+	I915_WRITE_FW(RING_ELSP(ring), desc[0]);
+	I915_WRITE_FW(RING_ELSP(ring), desc[3]);
 
 	/* The context is automatically loaded after the following */
-	I915_WRITE(RING_ELSP(ring), desc[2]);
+	I915_WRITE_FW(RING_ELSP(ring), desc[2]);
 
 	/* ELSP is a wo register, so use another nearby reg for posting instead */
-	POSTING_READ(RING_EXECLIST_STATUS(ring));
-	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
+	POSTING_READ_FW(RING_EXECLIST_STATUS(ring));
+	intel_uncore_forcewake_put__locked(dev_priv, FORCEWAKE_ALL);
+	spin_unlock(&dev_priv->uncore.lock);
 }
 
 static int execlists_update_context(struct drm_i915_gem_object *ctx_obj,

drivers/gpu/drm/i915/intel_uncore.c

@@ -375,6 +375,26 @@ void intel_uncore_sanitize(struct drm_device *dev)
 	intel_disable_gt_powersave(dev);
 }
 
+static void __intel_uncore_forcewake_get(struct drm_i915_private *dev_priv,
+					 enum forcewake_domains fw_domains)
+{
+	struct intel_uncore_forcewake_domain *domain;
+	enum forcewake_domain_id id;
+
+	if (!dev_priv->uncore.funcs.force_wake_get)
+		return;
+
+	fw_domains &= dev_priv->uncore.fw_domains;
+
+	for_each_fw_domain_mask(domain, fw_domains, dev_priv, id) {
+		if (domain->wake_count++)
+			fw_domains &= ~(1 << id);
+	}
+
+	if (fw_domains)
+		dev_priv->uncore.funcs.force_wake_get(dev_priv, fw_domains);
+}
+
 /**
  * intel_uncore_forcewake_get - grab forcewake domain references
  * @dev_priv: i915 device instance
@@ -392,41 +412,39 @@ void intel_uncore_forcewake_get(struct drm_i915_private *dev_priv,
 				enum forcewake_domains fw_domains)
 {
 	unsigned long irqflags;
-	struct intel_uncore_forcewake_domain *domain;
-	enum forcewake_domain_id id;
 
 	if (!dev_priv->uncore.funcs.force_wake_get)
 		return;
 
 	WARN_ON(dev_priv->pm.suspended);
 
-	fw_domains &= dev_priv->uncore.fw_domains;
-
 	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
-
-	for_each_fw_domain_mask(domain, fw_domains, dev_priv, id) {
-		if (domain->wake_count++)
-			fw_domains &= ~(1 << id);
-	}
-
-	if (fw_domains)
-		dev_priv->uncore.funcs.force_wake_get(dev_priv, fw_domains);
-
+	__intel_uncore_forcewake_get(dev_priv, fw_domains);
 	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
 }
 
 /**
- * intel_uncore_forcewake_put - release a forcewake domain reference
+ * intel_uncore_forcewake_get__locked - grab forcewake domain references
  * @dev_priv: i915 device instance
- * @fw_domains: forcewake domains to put references
+ * @fw_domains: forcewake domains to get reference on
  *
- * This function drops the device-level forcewakes for specified
- * domains obtained by intel_uncore_forcewake_get().
+ * See intel_uncore_forcewake_get(). This variant places the onus
+ * on the caller to explicitly handle the dev_priv->uncore.lock spinlock.
  */
-void intel_uncore_forcewake_put(struct drm_i915_private *dev_priv,
-				enum forcewake_domains fw_domains)
+void intel_uncore_forcewake_get__locked(struct drm_i915_private *dev_priv,
+					enum forcewake_domains fw_domains)
+{
+	assert_spin_locked(&dev_priv->uncore.lock);
+
+	if (!dev_priv->uncore.funcs.force_wake_get)
+		return;
+
+	__intel_uncore_forcewake_get(dev_priv, fw_domains);
+}
+
+static void __intel_uncore_forcewake_put(struct drm_i915_private *dev_priv,
+					 enum forcewake_domains fw_domains)
 {
-	unsigned long irqflags;
 	struct intel_uncore_forcewake_domain *domain;
 	enum forcewake_domain_id id;
 
@@ -435,8 +453,6 @@ void intel_uncore_forcewake_put(struct drm_i915_private *dev_priv,
 
 	fw_domains &= dev_priv->uncore.fw_domains;
 
-	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
-
 	for_each_fw_domain_mask(domain, fw_domains, dev_priv, id) {
 		if (WARN_ON(domain->wake_count == 0))
 			continue;
@@ -447,10 +463,48 @@ void intel_uncore_forcewake_put(struct drm_i915_private *dev_priv,
 		domain->wake_count++;
 		fw_domain_arm_timer(domain);
 	}
+}
 
+/**
+ * intel_uncore_forcewake_put - release a forcewake domain reference
+ * @dev_priv: i915 device instance
+ * @fw_domains: forcewake domains to put references
+ *
+ * This function drops the device-level forcewakes for specified
+ * domains obtained by intel_uncore_forcewake_get().
+ */
+void intel_uncore_forcewake_put(struct drm_i915_private *dev_priv,
+				enum forcewake_domains fw_domains)
+{
+	unsigned long irqflags;
+
+	if (!dev_priv->uncore.funcs.force_wake_put)
+		return;
+
+	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
+	__intel_uncore_forcewake_put(dev_priv, fw_domains);
 	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
 }
 
+/**
+ * intel_uncore_forcewake_put__locked - grab forcewake domain references
+ * @dev_priv: i915 device instance
+ * @fw_domains: forcewake domains to get reference on
+ *
+ * See intel_uncore_forcewake_put(). This variant places the onus
+ * on the caller to explicitly handle the dev_priv->uncore.lock spinlock.
+ */
+void intel_uncore_forcewake_put__locked(struct drm_i915_private *dev_priv,
+					enum forcewake_domains fw_domains)
+{
+	assert_spin_locked(&dev_priv->uncore.lock);
+
+	if (!dev_priv->uncore.funcs.force_wake_put)
+		return;
+
+	__intel_uncore_forcewake_put(dev_priv, fw_domains);
+}
+
 void assert_forcewakes_inactive(struct drm_i915_private *dev_priv)
 {
 	struct intel_uncore_forcewake_domain *domain;