drm/amdgpu/display: add flag for multi-display mclk switching

Add a dcfeaturemask flag for mclk switching. Disable by default;
enable once the feature has seen more testing.

Set amdgpu.dcfeaturemask=2 on the kernel command line in grub
to enable this.

Acked-by: Evan Quan <[e-mail]>
Reviewed-by: Nicholas Kazlauskas <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 	if (amdgpu_dc_feature_mask & DC_FBC_MASK)
 		init_data.flags.fbc_support = true;
 
+	if (amdgpu_dc_feature_mask & DC_MULTI_MON_PP_MCLK_SWITCH_MASK)
+		init_data.flags.multi_mon_pp_mclk_switch = true;
+
 	init_data.flags.power_down_display_on_boot = true;
 
 #ifdef CONFIG_DRM_AMD_DC_DCN2_0

drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c

···
 
 	populate_initial_data(pipe, pipe_count, data);
 
-	calcs_output->all_displays_in_sync = all_displays_in_sync(pipe, pipe_count);
+	if (ctx->dc->config.multi_mon_pp_mclk_switch)
+		calcs_output->all_displays_in_sync = all_displays_in_sync(pipe, pipe_count);
+	else
+		calcs_output->all_displays_in_sync = false;
 
 	if (data->number_of_displays != 0) {
 		uint8_t yclk_lvl, sclk_lvl;

drivers/gpu/drm/amd/display/dc/dc.h

···
 	bool power_down_display_on_boot;
 	bool edp_not_connected;
 	bool forced_clocks;
-
+	bool multi_mon_pp_mclk_switch;
 };
 
 enum visual_confirm {

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

···
 
 enum DC_FEATURE_MASK {
 	DC_FBC_MASK = 0x1,
+	DC_MULTI_MON_PP_MCLK_SWITCH_MASK = 0x2,
 };
 
 enum amd_dpm_forced_level;