drm/radeon: fix & improve ih ring handling v3

The spinlock was actually there to protect the
rptr, but rptr was read outside of the locked area.

Also we don't really need a spinlock here, an
atomic should to quite fine since we only need to
prevent it from being reentrant.

v2: Keep the spinlock....
v3: Back to an atomic again after finding & fixing the real bug.
Signed-off-by: Christian Koenig <christian.koenig@amd.com>

drivers/gpu/drm/radeon/evergreen.c

@@ -2676,7 +2676,6 @@ int evergreen_irq_process(struct radeon_device *rdev)
 	u32 rptr;
 	u32 src_id, src_data;
 	u32 ring_index;
-	unsigned long flags;
 	bool queue_hotplug = false;
 	bool queue_hdmi = false;
 
@@ -2684,22 +2683,21 @@ int evergreen_irq_process(struct radeon_device *rdev)
 		return IRQ_NONE;
 
 	wptr = evergreen_get_ih_wptr(rdev);
+
+restart_ih:
+	/* is somebody else already processing irqs? */
+	if (atomic_xchg(&rdev->ih.lock, 1))
+		return IRQ_NONE;
+
 	rptr = rdev->ih.rptr;
 	DRM_DEBUG("r600_irq_process start: rptr %d, wptr %d\n", rptr, wptr);
 
-	spin_lock_irqsave(&rdev->ih.lock, flags);
-	if (rptr == wptr) {
-		spin_unlock_irqrestore(&rdev->ih.lock, flags);
-		return IRQ_NONE;
-	}
-restart_ih:
 	/* Order reading of wptr vs. reading of IH ring data */
 	rmb();
 
 	/* display interrupts */
 	evergreen_irq_ack(rdev);
 
-	rdev->ih.wptr = wptr;
 	while (rptr != wptr) {
 		/* wptr/rptr are in bytes! */
 		ring_index = rptr / 4;
@@ -2998,17 +2996,19 @@ int evergreen_irq_process(struct radeon_device *rdev)
 		rptr += 16;
 		rptr &= rdev->ih.ptr_mask;
 	}
-	/* make sure wptr hasn't changed while processing */
-	wptr = evergreen_get_ih_wptr(rdev);
-	if (wptr != rdev->ih.wptr)
-		goto restart_ih;
 	if (queue_hotplug)
 		schedule_work(&rdev->hotplug_work);
 	if (queue_hdmi)
 		schedule_work(&rdev->audio_work);
 	rdev->ih.rptr = rptr;
 	WREG32(IH_RB_RPTR, rdev->ih.rptr);
-	spin_unlock_irqrestore(&rdev->ih.lock, flags);
+	atomic_set(&rdev->ih.lock, 0);
+
+	/* make sure wptr hasn't changed while processing */
+	wptr = evergreen_get_ih_wptr(rdev);
+	if (wptr != rptr)
+		goto restart_ih;
+
 	return IRQ_HANDLED;
 }
 

drivers/gpu/drm/radeon/r600.c

@@ -2858,7 +2858,6 @@ void r600_disable_interrupts(struct radeon_device *rdev)
 	WREG32(IH_RB_RPTR, 0);
 	WREG32(IH_RB_WPTR, 0);
 	rdev->ih.enabled = false;
-	rdev->ih.wptr = 0;
 	rdev->ih.rptr = 0;
 }
 
@@ -3310,7 +3309,6 @@ int r600_irq_process(struct radeon_device *rdev)
 	u32 rptr;
 	u32 src_id, src_data;
 	u32 ring_index;
-	unsigned long flags;
 	bool queue_hotplug = false;
 	bool queue_hdmi = false;
 
@@ -3322,24 +3320,21 @@ int r600_irq_process(struct radeon_device *rdev)
 		RREG32(IH_RB_WPTR);
 
 	wptr = r600_get_ih_wptr(rdev);
-	rptr = rdev->ih.rptr;
-	DRM_DEBUG("r600_irq_process start: rptr %d, wptr %d\n", rptr, wptr);
-
-	spin_lock_irqsave(&rdev->ih.lock, flags);
 
-	if (rptr == wptr) {
-		spin_unlock_irqrestore(&rdev->ih.lock, flags);
+restart_ih:
+	/* is somebody else already processing irqs? */
+	if (atomic_xchg(&rdev->ih.lock, 1))
 		return IRQ_NONE;
-	}
 
-restart_ih:
+	rptr = rdev->ih.rptr;
+	DRM_DEBUG("r600_irq_process start: rptr %d, wptr %d\n", rptr, wptr);
+
 	/* Order reading of wptr vs. reading of IH ring data */
 	rmb();
 
 	/* display interrupts */
 	r600_irq_ack(rdev);
 
-	rdev->ih.wptr = wptr;
 	while (rptr != wptr) {
 		/* wptr/rptr are in bytes! */
 		ring_index = rptr / 4;
@@ -3493,17 +3488,19 @@ int r600_irq_process(struct radeon_device *rdev)
 		rptr += 16;
 		rptr &= rdev->ih.ptr_mask;
 	}
-	/* make sure wptr hasn't changed while processing */
-	wptr = r600_get_ih_wptr(rdev);
-	if (wptr != rdev->ih.wptr)
-		goto restart_ih;
 	if (queue_hotplug)
 		schedule_work(&rdev->hotplug_work);
 	if (queue_hdmi)
 		schedule_work(&rdev->audio_work);
 	rdev->ih.rptr = rptr;
 	WREG32(IH_RB_RPTR, rdev->ih.rptr);
-	spin_unlock_irqrestore(&rdev->ih.lock, flags);
+	atomic_set(&rdev->ih.lock, 0);
+
+	/* make sure wptr hasn't changed while processing */
+	wptr = r600_get_ih_wptr(rdev);
+	if (wptr != rptr)
+		goto restart_ih;
+
 	return IRQ_HANDLED;
 }
 

drivers/gpu/drm/radeon/radeon.h

@@ -738,11 +738,10 @@ struct r600_ih {
 	struct radeon_bo	*ring_obj;
 	volatile uint32_t	*ring;
 	unsigned		rptr;
-	unsigned		wptr;
 	unsigned		ring_size;
 	uint64_t		gpu_addr;
 	uint32_t		ptr_mask;
-	spinlock_t              lock;
+	atomic_t		lock;
 	bool                    enabled;
 };
 

drivers/gpu/drm/radeon/radeon_device.c

@@ -731,8 +731,7 @@ int radeon_device_init(struct radeon_device *rdev,
 	radeon_mutex_init(&rdev->cs_mutex);
 	mutex_init(&rdev->ring_lock);
 	mutex_init(&rdev->dc_hw_i2c_mutex);
-	if (rdev->family >= CHIP_R600)
-		spin_lock_init(&rdev->ih.lock);
+	atomic_set(&rdev->ih.lock, 0);
 	mutex_init(&rdev->gem.mutex);
 	mutex_init(&rdev->pm.mutex);
 	init_rwsem(&rdev->pm.mclk_lock);

drivers/gpu/drm/radeon/si.c

@@ -2942,7 +2942,6 @@ static void si_disable_interrupts(struct radeon_device *rdev)
 	WREG32(IH_RB_RPTR, 0);
 	WREG32(IH_RB_WPTR, 0);
 	rdev->ih.enabled = false;
-	rdev->ih.wptr = 0;
 	rdev->ih.rptr = 0;
 }
 
@@ -3359,29 +3358,27 @@ int si_irq_process(struct radeon_device *rdev)
 	u32 rptr;
 	u32 src_id, src_data, ring_id;
 	u32 ring_index;
-	unsigned long flags;
 	bool queue_hotplug = false;
 
 	if (!rdev->ih.enabled || rdev->shutdown)
 		return IRQ_NONE;
 
 	wptr = si_get_ih_wptr(rdev);
+
+restart_ih:
+	/* is somebody else already processing irqs? */
+	if (atomic_xchg(&rdev->ih.lock, 1))
+		return IRQ_NONE;
+
 	rptr = rdev->ih.rptr;
 	DRM_DEBUG("si_irq_process start: rptr %d, wptr %d\n", rptr, wptr);
 
-	spin_lock_irqsave(&rdev->ih.lock, flags);
-	if (rptr == wptr) {
-		spin_unlock_irqrestore(&rdev->ih.lock, flags);
-		return IRQ_NONE;
-	}
-restart_ih:
 	/* Order reading of wptr vs. reading of IH ring data */
 	rmb();
 
 	/* display interrupts */
 	si_irq_ack(rdev);
 
-	rdev->ih.wptr = wptr;
 	while (rptr != wptr) {
 		/* wptr/rptr are in bytes! */
 		ring_index = rptr / 4;
@@ -3632,15 +3629,17 @@ int si_irq_process(struct radeon_device *rdev)
 		rptr += 16;
 		rptr &= rdev->ih.ptr_mask;
 	}
-	/* make sure wptr hasn't changed while processing */
-	wptr = si_get_ih_wptr(rdev);
-	if (wptr != rdev->ih.wptr)
-		goto restart_ih;
 	if (queue_hotplug)
 		schedule_work(&rdev->hotplug_work);
 	rdev->ih.rptr = rptr;
 	WREG32(IH_RB_RPTR, rdev->ih.rptr);
-	spin_unlock_irqrestore(&rdev->ih.lock, flags);
+	atomic_set(&rdev->ih.lock, 0);
+
+	/* make sure wptr hasn't changed while processing */
+	wptr = si_get_ih_wptr(rdev);
+	if (wptr != rptr)
+		goto restart_ih;
+
 	return IRQ_HANDLED;
 }