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>

1 files changed, 13 insertions, 14 deletions

diff --git a/drivers/gpu/drm/radeon/si.c b/drivers/gpu/drm/radeon/si.c
index 8868a1fa20e5..ecef972050d1 100644
--- a/drivers/gpu/drm/radeon/si.c
+++ b/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 @@ restart_ih:
 		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;
 }