[PATCH] drm/gem-shmem: Optimize DMA mapping for exported buffers

[Jacek Lawrynowicz]

Use DMA_ATTR_SKIP_CPU_SYNC flag for exported buffers during DMA mapping.
The same flag is already used by drm_gem_map_dma_buf() for imported
buffers.

Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz at linux.intel.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c |  8 ++++++--
 include/drm/drm_gem.h                  | 12 ++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index d99dee67353a1..8938d8e3de52f 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -699,7 +699,7 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_get_sg_table);
 static struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_object *shmem)
 {
 	struct drm_gem_object *obj = &shmem->base;
-	int ret;
+	int ret, flags = 0;
 	struct sg_table *sgt;
 
 	if (shmem->sgt)
@@ -716,8 +716,12 @@ static struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_
 		ret = PTR_ERR(sgt);
 		goto err_put_pages;
 	}
+
+	if (drm_gem_is_exported())
+		flags |= DMA_ATTR_SKIP_CPU_SYNC;
+
 	/* Map the pages for use by the h/w. */
-	ret = dma_map_sgtable(obj->dev->dev, sgt, DMA_BIDIRECTIONAL, 0);
+	ret = dma_map_sgtable(obj->dev->dev, sgt, DMA_BIDIRECTIONAL, flags);
 	if (ret)
 		goto err_free_sgt;
 
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 2bf893eabb4b2..7c355a44d0a49 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -589,6 +589,18 @@ static inline bool drm_gem_is_imported(const struct drm_gem_object *obj)
 	return obj->dma_buf && (obj->dma_buf->priv != obj);
 }
 
+/**
+ * drm_gem_is_exported() - Tests if GEM object's buffer has been exported
+ * @obj: the GEM object
+ *
+ * Returns:
+ * True if the GEM object's buffer has been exported, false otherwise
+ */
+static inline bool drm_gem_is_exported(const struct drm_gem_object *obj)
+{
+	return obj->dma_buf && (obj->dma_buf->priv == obj);
+}
+
 #ifdef CONFIG_LOCKDEP
 /**
  * drm_gem_gpuva_set_lock() - Set the lock protecting accesses to the gpuva list.
-- 
2.45.1