drm/xe: Make irq enabled flag atomic

The irq.enabled flag was protected by a spin lock (irq.lock).
By making it atomic we no longer need to wait for the spin lock in
irq handlers. This will become especially useful for MSI-X irq
handlers to prevent lock contention between different interrupts.

Signed-off-by: Ilia Levi <[email protected]>
Reviewed-by: Rodrigo Vivi <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Rodrigo Vivi <[email protected]>

Author: illevi

drivers/gpu/drm/xe/display/ext/i915_irq.c

@@ -53,18 +53,7 @@ void gen2_irq_init(struct intel_uncore *uncore, struct i915_irq_regs regs,
 
 bool intel_irqs_enabled(struct xe_device *xe)
 {
-	/*
-	 * XXX: i915 has a racy handling of the irq.enabled, since it doesn't
-	 * lock its transitions. Because of that, the irq.enabled sometimes
-	 * is not read with the irq.lock in place.
-	 * However, the most critical cases like vblank and page flips are
-	 * properly using the locks.
-	 * We cannot take the lock in here or run any kind of assert because
-	 * of i915 inconsistency.
-	 * But at this point the xe irq is better protected against races,
-	 * although the full solution would be protecting the i915 side.
-	 */
-	return xe->irq.enabled;
+	return atomic_read(&xe->irq.enabled);
 }
 
 void intel_synchronize_irq(struct xe_device *xe)

drivers/gpu/drm/xe/xe_device_types.h

@@ -347,7 +347,7 @@ struct xe_device {
 		spinlock_t lock;
 
 		/** @irq.enabled: interrupts enabled on this device */
-		bool enabled;
+		atomic_t enabled;
 	} irq;
 
 	/** @ttm: ttm device */

drivers/gpu/drm/xe/xe_irq.c

@@ -348,12 +348,8 @@ static irqreturn_t xelp_irq_handler(int irq, void *arg)
 	unsigned long intr_dw[2];
 	u32 identity[32];
 
-	spin_lock(&xe->irq.lock);
-	if (!xe->irq.enabled) {
-		spin_unlock(&xe->irq.lock);
+	if (!atomic_read(&xe->irq.enabled))
 		return IRQ_NONE;
-	}
-	spin_unlock(&xe->irq.lock);
 
 	master_ctl = xelp_intr_disable(xe);
 	if (!master_ctl) {
@@ -417,12 +413,8 @@ static irqreturn_t dg1_irq_handler(int irq, void *arg)
 
 	/* TODO: This really shouldn't be copied+pasted */
 
-	spin_lock(&xe->irq.lock);
-	if (!xe->irq.enabled) {
-		spin_unlock(&xe->irq.lock);
+	if (!atomic_read(&xe->irq.enabled))
 		return IRQ_NONE;
-	}
-	spin_unlock(&xe->irq.lock);
 
 	master_tile_ctl = dg1_intr_disable(xe);
 	if (!master_tile_ctl) {
@@ -644,12 +636,8 @@ static irqreturn_t vf_mem_irq_handler(int irq, void *arg)
 	struct xe_tile *tile;
 	unsigned int id;
 
-	spin_lock(&xe->irq.lock);
-	if (!xe->irq.enabled) {
-		spin_unlock(&xe->irq.lock);
+	if (!atomic_read(&xe->irq.enabled))
 		return IRQ_NONE;
-	}
-	spin_unlock(&xe->irq.lock);
 
 	for_each_tile(tile, xe, id)
 		xe_memirq_handler(&tile->memirq);
@@ -674,10 +662,9 @@ static void irq_uninstall(void *arg)
 	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
 	int irq;
 
-	if (!xe->irq.enabled)
+	if (!atomic_xchg(&xe->irq.enabled, 0))
 		return;
 
-	xe->irq.enabled = false;
 	xe_irq_reset(xe);
 
 	irq = pci_irq_vector(pdev, 0);
@@ -724,7 +711,7 @@ int xe_irq_install(struct xe_device *xe)
 		return err;
 	}
 
-	xe->irq.enabled = true;
+	atomic_set(&xe->irq.enabled, 1);
 
 	xe_irq_postinstall(xe);
 
@@ -744,9 +731,7 @@ void xe_irq_suspend(struct xe_device *xe)
 {
 	int irq = to_pci_dev(xe->drm.dev)->irq;
 
-	spin_lock_irq(&xe->irq.lock);
-	xe->irq.enabled = false; /* no new irqs */
-	spin_unlock_irq(&xe->irq.lock);
+	atomic_set(&xe->irq.enabled, 0); /* no new irqs */
 
 	synchronize_irq(irq); /* flush irqs */
 	xe_irq_reset(xe); /* turn irqs off */
@@ -762,7 +747,7 @@ void xe_irq_resume(struct xe_device *xe)
 	 * 1. no irq will arrive before the postinstall
 	 * 2. display is not yet resumed
 	 */
-	xe->irq.enabled = true;
+	atomic_set(&xe->irq.enabled, 1);
 	xe_irq_reset(xe);
 	xe_irq_postinstall(xe); /* turn irqs on */