dma-buf: add enum dma_resv_usage v4

This change adds the dma_resv_usage enum and allows us to specify why a
dma_resv object is queried for its containing fences.

Additional to that a dma_resv_usage_rw() helper function is added to aid
retrieving the fences for a read or write userspace submission.

This is then deployed to the different query functions of the dma_resv
object and all of their users. When the write paratermer was previously
true we now use DMA_RESV_USAGE_WRITE and DMA_RESV_USAGE_READ otherwise.

v2: add KERNEL/OTHER in separate patch
v3: some kerneldoc suggestions by Daniel
v4: some more kerneldoc suggestions by Daniel, fix missing cases lost in
    the rebase pointed out by Bas.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220407085946.744568-2-christian.koenig@amd.com

1 files changed, 6 insertions, 2 deletions

diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 6fb91956ab8d..a297397743a2 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -408,6 +408,9 @@ struct dma_buf {
 	 *   pipelining across drivers. These do not set any fences for their
 	 *   access. An example here is v4l.
 	 *
+	 * - Driver should use dma_resv_usage_rw() when retrieving fences as
+	 *   dependency for implicit synchronization.
+	 *
 	 * DYNAMIC IMPORTER RULES:
 	 *
 	 * Dynamic importers, see dma_buf_attachment_is_dynamic(), have
@@ -423,8 +426,9 @@ struct dma_buf {
 	 *
 	 * IMPORTANT:
 	 *
-	 * All drivers must obey the struct dma_resv rules, specifically the
-	 * rules for updating and obeying fences.
+	 * All drivers and memory management related functions must obey the
+	 * struct dma_resv rules, specifically the rules for updating and
+	 * obeying fences. See enum dma_resv_usage for further descriptions.
 	 */
 	struct dma_resv *resv;