drm/amdgpu: restrict the sched jobs number to power of two

BugLink: http://bugs.launchpad.net/bugs/1546572Signed-off-by: Chunming Zhou <David1.Zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
CC: stable@vger.kernel.org
(cherry picked from commit 5b011235)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c

@@ -252,7 +252,7 @@ uint64_t amdgpu_ctx_add_fence(struct amdgpu_ctx *ctx, struct amdgpu_ring *ring,
 	unsigned idx = 0;
 	struct fence *other = NULL;
 
-	idx = seq % amdgpu_sched_jobs;
+	idx = seq & (amdgpu_sched_jobs - 1);
 	other = cring->fences[idx];
 	if (other) {
 		signed long r;
@@ -292,7 +292,7 @@ struct fence *amdgpu_ctx_get_fence(struct amdgpu_ctx *ctx,
 		return NULL;
 	}
 
-	fence = fence_get(cring->fences[seq % amdgpu_sched_jobs]);
+	fence = fence_get(cring->fences[seq & (amdgpu_sched_jobs - 1)]);
 	spin_unlock(&ctx->ring_lock);
 
 	return fence;

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

@@ -949,6 +949,15 @@ static bool amdgpu_check_pot_argument(int arg)
  */
 static void amdgpu_check_arguments(struct amdgpu_device *adev)
 {
+	if (amdgpu_sched_jobs < 4) {
+		dev_warn(adev->dev, "sched jobs (%d) must be at least 4\n",
+			 amdgpu_sched_jobs);
+		amdgpu_sched_jobs = 4;
+	} else if (!amdgpu_check_pot_argument(amdgpu_sched_jobs)){
+		dev_warn(adev->dev, "sched jobs (%d) must be a power of 2\n",
+			 amdgpu_sched_jobs);
+		amdgpu_sched_jobs = roundup_pow_of_two(amdgpu_sched_jobs);
+	}
 	/* vramlimit must be a power of two */
 	if (!amdgpu_check_pot_argument(amdgpu_vram_limit)) {
 		dev_warn(adev->dev, "vram limit (%d) must be a power of 2\n",