drm/radeon: fix a bug with the ring syncing code

Rings need to lock in order, otherwise
the ring subsystem can deadlock.

v2: fix error handling and number of locked doublewords.
v3: stop creating unneeded semaphores.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 56 insertions, 0 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_semaphore.c b/drivers/gpu/drm/radeon/radeon_semaphore.c
index 61dd4e3c9209..930a08af900f 100644
--- a/drivers/gpu/drm/radeon/radeon_semaphore.c
+++ b/drivers/gpu/drm/radeon/radeon_semaphore.c
@@ -149,6 +149,62 @@ void radeon_semaphore_emit_wait(struct radeon_device *rdev, int ring,
         radeon_semaphore_ring_emit(rdev, ring, &rdev->ring[ring], semaphore, true);
 }
 
+int radeon_semaphore_sync_rings(struct radeon_device *rdev,
+                                struct radeon_semaphore *semaphore,
+                                bool sync_to[RADEON_NUM_RINGS],
+                                int dst_ring)
+{
+        int i, r;
+
+        for (i = 0; i < RADEON_NUM_RINGS; ++i) {
+                unsigned num_ops = i == dst_ring ? RADEON_NUM_RINGS : 1;
+
+                /* don't lock unused rings */
+                if (!sync_to[i] && i != dst_ring)
+                        continue;
+
+                /* prevent GPU deadlocks */
+                if (!rdev->ring[i].ready) {
+                        dev_err(rdev->dev, "Trying to sync to a disabled ring!");
+                        r = -EINVAL;
+                        goto error;
+                }
+
+                r = radeon_ring_lock(rdev, &rdev->ring[i], num_ops * 8);
+                if (r)
+                        goto error;
+        }
+
+        for (i = 0; i < RADEON_NUM_RINGS; ++i) {
+                /* no need to sync to our own or unused rings */
+                if (!sync_to[i] || i == dst_ring)
+                        continue;
+
+                radeon_semaphore_emit_signal(rdev, i, semaphore);
+                radeon_semaphore_emit_wait(rdev, dst_ring, semaphore);
+        }
+
+        for (i = 0; i < RADEON_NUM_RINGS; ++i) {
+
+                /* don't unlock unused rings */
+                if (!sync_to[i] && i != dst_ring)
+                        continue;
+
+                radeon_ring_unlock_commit(rdev, &rdev->ring[i]);
+        }
+
+        return 0;
+
+error:
+        /* unlock all locks taken so far */
+        for (--i; i >= 0; --i) {
+                if (sync_to[i] || i == dst_ring) {
+                        radeon_ring_unlock_undo(rdev, &rdev->ring[i]);
+                }
+        }
+        return r;
+}
+
 void radeon_semaphore_free(struct radeon_device *rdev,
                            struct radeon_semaphore *semaphore)
 {