[PATCH 1/2] drm/sched: add DRM_SCHED_FENCE_DONT_PIPELINE flag

[Christian König]

Setting this flag on a scheduler fence prevents pipelining of jobs
depending on this fence. In other words we always insert a full CPU
round trip before dependen jobs are pushed to the pipeline.

Signed-off-by: Christian König <christian.koenig at amd.com>
CC: stable at vger.kernel.org # 5.19+
---
 drivers/gpu/drm/scheduler/sched_entity.c | 3 ++-
 include/drm/gpu_scheduler.h              | 9 +++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index 191c56064f19..43d337d8b153 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -385,7 +385,8 @@ static bool drm_sched_entity_add_dependency_cb(struct drm_sched_entity *entity)
 	}
 
 	s_fence = to_drm_sched_fence(fence);
-	if (s_fence && s_fence->sched == sched) {
+	if (s_fence && s_fence->sched == sched &&
+	    !test_bit(DRM_SCHED_FENCE_DONT_PIPELINE, &fence->flags)) {
 
 		/*
 		 * Fence is from the same scheduler, only need to wait for
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index 0fca8f38bee4..f01d14b231ed 100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -32,6 +32,15 @@
 
 #define MAX_WAIT_SCHED_ENTITY_Q_EMPTY msecs_to_jiffies(1000)
 
+/**
+ * DRM_SCHED_FENCE_DONT_PIPELINE - Prefent dependency pipelining
+ *
+ * Setting this flag on a scheduler fence prevents pipelining of jobs depending
+ * on this fence. In other words we always insert a full CPU round trip before
+ * dependen jobs are pushed to the hw queue.
+ */
+#define DRM_SCHED_FENCE_DONT_PIPELINE	DMA_FENCE_FLAG_USER_BITS
+
 struct drm_gem_object;
 
 struct drm_gpu_scheduler;
-- 
2.25.1