drm/amd/display: Add dcdebugmask option for disabling MPO

[Why & How]

It's useful to disable MPO when debugging or testing. Therefore, add a
dcdebugmask option to disable MPO.

Signed-off-by: Leo Li <[e-mail]>
Reviewed-by: Rodrigo Siqueira <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

···
 	for (i = 0; i < dm->dc->caps.max_planes; ++i) {
 		struct dc_plane_cap *plane = &dm->dc->caps.planes[i];
 
+		/* Do not create overlay if MPO disabled */
+		if (amdgpu_dc_debug_mask & DC_DISABLE_MPO)
+			break;
+
 		if (plane->type != DC_PLANE_TYPE_DCN_UNIVERSAL)
 			continue;
 

drivers/gpu/drm/amd/include/amd_shared.h

···
 	DC_DISABLE_CLOCK_GATING = 0x8,
 	DC_DISABLE_PSR = 0x10,
 	DC_FORCE_SUBVP_MCLK_SWITCH = 0x20,
+	DC_DISABLE_MPO = 0x40,
 };
 
 enum amd_dpm_forced_level;