drm/amdgpu: reject gang submissions under SRIOV

[ Upstream commit d7ddcf921e ]

Gang submission means that the kernel driver guarantees that multiple
submissions are executed on the HW at the same time on different engines.

Background is that those submissions then depend on each other and each
can't finish stand alone.

SRIOV now uses world switch to preempt submissions on the engines to allow
sharing the HW resources between multiple VFs.

The problem is now that the SRIOV world switch can't know about such inter
dependencies and will cause a timeout if it waits for a partially running
gang submission.

To conclude SRIOV and gang submissions are fundamentally incompatible at
the moment. For now just disable them.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

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

@@ -286,7 +286,7 @@ static int amdgpu_cs_pass1(struct amdgpu_cs_parser *p,
 		}
 	}
 
-	if (!p->gang_size) {
+	if (!p->gang_size || (amdgpu_sriov_vf(p->adev) && p->gang_size > 1)) {
 		ret = -EINVAL;
 		goto free_all_kdata;
 	}