drm/amdgpu: disable mcbp if parameter zero is set

The parameter amdgpu_mcbp shall have priority against the default value
calculated from the chip version.
User could disable mcbp by setting the parameter mcbp as zero.

v2: do not trigger preemption in sw ring muxer when mcbp is disabled.
Signed-off-by: Jiadong Zhu <Jiadong.Zhu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -3722,10 +3722,11 @@ static void amdgpu_device_set_mcbp(struct amdgpu_device *adev)
 {
 	if (amdgpu_mcbp == 1)
 		adev->gfx.mcbp = true;
-
-	if ((adev->ip_versions[GC_HWIP][0] >= IP_VERSION(9, 0, 0)) &&
-	    (adev->ip_versions[GC_HWIP][0] < IP_VERSION(10, 0, 0)) &&
-	    adev->gfx.num_gfx_rings)
+	else if (amdgpu_mcbp == 0)
+		adev->gfx.mcbp = false;
+	else if ((adev->ip_versions[GC_HWIP][0] >= IP_VERSION(9, 0, 0)) &&
+		 (adev->ip_versions[GC_HWIP][0] < IP_VERSION(10, 0, 0)) &&
+		 adev->gfx.num_gfx_rings)
 		adev->gfx.mcbp = true;
 
 	if (amdgpu_sriov_vf(adev))

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

@@ -397,7 +397,7 @@ void amdgpu_sw_ring_ib_begin(struct amdgpu_ring *ring)
 	struct amdgpu_ring_mux *mux = &adev->gfx.muxer;
 
 	WARN_ON(!ring->is_sw_ring);
-	if (ring->hw_prio > AMDGPU_RING_PRIO_DEFAULT) {
+	if (adev->gfx.mcbp && ring->hw_prio > AMDGPU_RING_PRIO_DEFAULT) {
 		if (amdgpu_mcbp_scan(mux) > 0)
 			amdgpu_mcbp_trigger_preempt(mux);
 		return;