Re: [Linaro-mm-sig] [PATCH] dma-buf/dma_resv_usage: update explicit sync documentation

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Am 12.07.22 um 15:20 schrieb Alex Deucher:
On Tue, Jul 12, 2022 at 9:12 AM Christian König
<ckoenig.leichtzumerken@xxxxxxxxx> wrote:
Make it clear that DMA_RESV_USAGE_BOOKMARK can be used for explicit synced
DMA_RESV_USAGE_BOOKKEEP?

Crappy autocorrect and copy&paste. Thanks for pointing that out.

Christian.


user space submissions as well and document the rules around adding the
same fence with different usages.

Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
  include/linux/dma-resv.h | 16 +++++++++++++---
  1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
index c8ccbc94d5d2..264e27e56dff 100644
--- a/include/linux/dma-resv.h
+++ b/include/linux/dma-resv.h
@@ -62,6 +62,11 @@ struct dma_resv_list;
   * For example when asking for WRITE fences then the KERNEL fences are returned
   * as well. Similar when asked for READ fences then both WRITE and KERNEL
   * fences are returned as well.
+ *
+ * Already used fences can be promoted in the sense that a fence with
+ * DMA_RESV_USAGE_BOOKMARK could become DMA_RESV_USAGE_READ by adding it again
Same here.

With that fixed,
Acked-by: Alex Deucher <alexander.deucher@xxxxxxx>

Alex

+ * with this usage. But fences can never be degraded in the sense that a fence
+ * with DMA_RESV_USAGE_WRITE could become DMA_RESV_USAGE_READ.
   */
  enum dma_resv_usage {
         /**
@@ -98,10 +103,15 @@ enum dma_resv_usage {
          * @DMA_RESV_USAGE_BOOKKEEP: No implicit sync.
          *
          * This should be used by submissions which don't want to participate in
-        * implicit synchronization.
+        * any implicit synchronization.
+        *
+        * The most common case are preemption fences, page table updates, TLB
+        * flushes as well as explicit synced user submissions.
          *
-        * The most common case are preemption fences as well as page table
-        * updates and their TLB flushes.
+        * Explicit synced user user submissions can be promoted to
+        * DMA_RESV_USAGE_READ or DMA_RESV_USAGE_WRITE as needed using
+        * dma_buf_import_sync_file() when implicit synchronization should
+        * become necessary after initial adding of the fence.
          */
         DMA_RESV_USAGE_BOOKKEEP
  };
--
2.25.1

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