[Intel-gfx] [PATCH 118/190] drm/i915: Remove locking for get_tiling

[Chris Wilson]

Since we are not concerned with userspace racing itself with set-tiling
(the order is indeterminant even if we take a lock), then we can safely
read back the single obj->tiling_mode and do the static lookup of
swizzle mode without having to take a lock.

get-tiling is reasonably frequent due to the back-channel passing around
of tiling parameters in DRI2/DRI3.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_tiling.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
index c7588135a82d..387246f19ce2 100644
--- a/drivers/gpu/drm/i915/i915_gem_tiling.c
+++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
@@ -301,10 +301,8 @@ i915_gem_get_tiling(struct drm_device *dev, void *data,
 	if (&obj->base == NULL)
 		return -ENOENT;
 
-	mutex_lock(&dev->struct_mutex);
-
 	args->tiling_mode = obj->tiling_mode;
-	switch (obj->tiling_mode) {
+	switch (args->tiling_mode) {
 	case I915_TILING_X:
 		args->swizzle_mode = dev_priv->mm.bit_6_swizzle_x;
 		break;
@@ -328,8 +326,6 @@ i915_gem_get_tiling(struct drm_device *dev, void *data,
 	if (args->swizzle_mode == I915_BIT_6_SWIZZLE_9_10_17)
 		args->swizzle_mode = I915_BIT_6_SWIZZLE_9_10;
 
-	drm_gem_object_unreference(&obj->base);
-	mutex_unlock(&dev->struct_mutex);
-
+	drm_gem_object_unreference_unlocked(&obj->base);
 	return 0;
 }
-- 
2.7.0.rc3