gpu: nvgpu: support skipping buffer refcounting in submit

In job submission path, we always take refcount on all
the mapped buffers to safeguard against case where user
space releases the buffer early

But in case user space itself is doing proper buffer
management, kernel need not take refcounts on all the
buffers - which is also a overhead in submit path

Hence, provide a new submit flag
NVGPU_SUBMIT_GPFIFO_FLAGS_SKIP_BUFFER_REFCOUNTING to
optionally skip taking refcounts on all the buffers

Also, if we do not take refcounts, then no need to drop
any refcounts in gk20a_channel_update() as well

Bug 1698667
Bug 200141116

Change-Id: I81bb7a03240300b691c70bcec04ea1badd5934f4
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/824718
(cherry picked from commit 8c8978fa303ec4e6db0233becdbdcbad4a248173)
Reviewed-on: http://git-master/r/835801
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/uapi/linux/nvgpu.h b/include/uapi/linux/nvgpu.h
index d2b5ceb8..025f2c9b 100644
--- a/include/uapi/linux/nvgpu.h
+++ b/include/uapi/linux/nvgpu.h
@@ -669,6 +669,8 @@ struct nvgpu_fence {
 #define NVGPU_SUBMIT_GPFIFO_FLAGS_SYNC_FENCE    (1 << 3)
 /* suppress WFI before fence trigger */
 #define NVGPU_SUBMIT_GPFIFO_FLAGS_SUPPRESS_WFI  (1 << 4)
+/* skip buffer refcounting during submit */
+#define NVGPU_SUBMIT_GPFIFO_FLAGS_SKIP_BUFFER_REFCOUNTING       (1 << 5)
 
 struct nvgpu_submit_gpfifo_args {
         __u64 gpfifo;