dma-resv: some doc polish for iterators

Hammer it a bit more in that iterators can be restarted and when that
matters, plus suggest to prefer the locked version whenver.

Also delete the two leftover kerneldoc for static functions plus
sprinkle some more links while at it.

v2: Keep some comments (Christian)

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20211130152756.1388106-1-daniel.vetter@ffwll.ch

1 files changed, 12 insertions, 1 deletions

diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
index a715df97b31a..afdfdfac729f 100644
--- a/include/linux/dma-resv.h
+++ b/include/linux/dma-resv.h
@@ -153,6 +153,13 @@ struct dma_resv {
  * struct dma_resv_iter - current position into the dma_resv fences
  *
  * Don't touch this directly in the driver, use the accessor function instead.
+ *
+ * IMPORTANT
+ *
+ * When using the lockless iterators like dma_resv_iter_next_unlocked() or
+ * dma_resv_for_each_fence_unlocked() beware that the iterator can be restarted.
+ * Code which accumulates statistics or similar needs to check for this with
+ * dma_resv_iter_is_restarted().
  */
 struct dma_resv_iter {
 	/** @obj: The dma_resv object we iterate over */
@@ -243,7 +250,11 @@ static inline bool dma_resv_iter_is_restarted(struct dma_resv_iter *cursor)
  * &dma_resv.lock and using RCU instead. The cursor needs to be initialized
  * with dma_resv_iter_begin() and cleaned up with dma_resv_iter_end(). Inside
  * the iterator a reference to the dma_fence is held and the RCU lock dropped.
- * When the dma_resv is modified the iteration starts over again.
+ *
+ * Beware that the iterator can be restarted when the struct dma_resv for
+ * @cursor is modified. Code which accumulates statistics or similar needs to
+ * check for this with dma_resv_iter_is_restarted(). For this reason prefer the
+ * lock iterator dma_resv_for_each_fence() whenever possible.
  */
 #define dma_resv_for_each_fence_unlocked(cursor, fence)			\
 	for (fence = dma_resv_iter_first_unlocked(cursor);		\