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Commit 9ad36761 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915: Remove locking for get_tiling 



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.

v2: Make tiling_mode a full unsigned int so that we can trivially use it
with READ_ONCE(). Separating it out into manual control over the flags
field was too noisy for a simple patch. Note that we could use the lower
bits of obj->stride for the tiling mode.

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470388464-28458-16-git-send-email-chris@chris-wilson.co.uk
parent e883d735

drivers/gpu/drm/i915/i915_drv.h

+8 −7
Original line number Diff line number Diff line
@@ -2182,10 +2182,6 @@ struct drm_i915_gem_object { 
	 */

	unsigned int madv:2;



	/**

	 * Current tiling mode for the object.

	 */

	unsigned int tiling_mode:2;

	/**

	 * Whether the tiling parameters for the currently associated fence

	 * register have changed. Note that for the purposes of tracking
@@ -2218,6 +2214,14 @@ struct drm_i915_gem_object { 


	atomic_t frontbuffer_bits;



	/**

	 * Current tiling mode for the object.

	 */

	unsigned int tiling_mode;



	/** Current tiling stride for the object, if it's tiled. */

	uint32_t stride;



	unsigned int has_wc_mmap;

	/** Count of VMA actually bound by this object */

	unsigned int bind_count;
@@ -2245,9 +2249,6 @@ struct drm_i915_gem_object { 
	struct i915_gem_active last_write;

	struct i915_gem_active last_fence;



	/** Current tiling stride for the object, if it's tiled. */

	uint32_t stride;



	/** References from framebuffers, locks out tiling changes. */

	unsigned long framebuffer_references;

drivers/gpu/drm/i915/i915_gem_tiling.c

+3 −7
Original line number Diff line number Diff line
@@ -303,10 +303,8 @@ i915_gem_get_tiling(struct drm_device *dev, void *data, 
	if (!obj)

		return -ENOENT;



	mutex_lock(&dev->struct_mutex);



	args->tiling_mode = obj->tiling_mode;

	switch (obj->tiling_mode) {

	args->tiling_mode = READ_ONCE(obj->tiling_mode);

	switch (args->tiling_mode) {

	case I915_TILING_X:

		args->swizzle_mode = dev_priv->mm.bit_6_swizzle_x;

		break;
@@ -330,8 +328,6 @@ 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;



	i915_gem_object_put(obj);

	mutex_unlock(&dev->struct_mutex);



	i915_gem_object_put_unlocked(obj);

	return 0;

}