drm/amd/display: Add module parameter for freesync video mode

[Why]
This option shall be opt-in by default since it is a temporary solution
until long term solution is agreed upon which may require userspace interface
changes. This feature give the user a seamless experience when freesync aware
programs (media players for instance) switches to a compatible freesync mode
when playing videos. Enabling this feature also have the potential side effect
of causing higher power consumption due to running a mode with lower resolution
and base clock frequency with the highest base clock supported on the monitor as
per its advertised modes. There has been precedent of manufacturing modes in the
kernel. In AMDGPU, the existing usage are for common modes and scaling modes.
Other driver have a similar approach as well.

[How]
Adds a module parameter to enable freesync video mode modeset
optimization. Enabling this mode allows the driver to skip a full modeset when a
freesync compatible mode is requested by the userspace. This parameter will also
add some additional modes that are within the connected monitor's VRR range
corresponding to common video modes, which media players can use for a seamless
experience while making use of freesync.

Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Shashank Sharma <shashank.sharma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -178,6 +178,7 @@ extern int amdgpu_gpu_recovery;
 extern int amdgpu_emu_mode;
 extern uint amdgpu_smu_memory_pool_size;
 extern uint amdgpu_dc_feature_mask;
+extern uint amdgpu_freesync_vid_mode;
 extern uint amdgpu_dc_debug_mask;
 extern uint amdgpu_dm_abm_level;
 extern struct amdgpu_mgpu_info mgpu_info;

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

@@ -163,6 +163,7 @@ int amdgpu_mes;
 int amdgpu_noretry = -1;
 int amdgpu_force_asic_type = -1;
 int amdgpu_tmz;
+uint amdgpu_freesync_vid_mode;
 int amdgpu_reset_method = -1; /* auto */
 int amdgpu_num_kcq = -1;
 
@@ -791,6 +792,17 @@ module_param_named(abmlevel, amdgpu_dm_abm_level, uint, 0444);
 MODULE_PARM_DESC(tmz, "Enable TMZ feature (-1 = auto, 0 = off (default), 1 = on)");
 module_param_named(tmz, amdgpu_tmz, int, 0444);
 
+/**
+ * DOC: freesync_video (uint)
+ * Enabled the optimization to adjust front porch timing to achieve seamless mode change experience
+ * when setting a freesync supported mode for which full modeset is not needed.
+ * The default value: 0 (off).
+ */
+MODULE_PARM_DESC(
+	freesync_video,
+	"Enable freesync modesetting optimization feature (0 = off (default), 1 = on)");
+module_param_named(freesync_video, amdgpu_freesync_vid_mode, uint, 0444);
+
 /**
  * DOC: reset_method (int)
  * GPU reset method (-1 = auto (default), 0 = legacy, 1 = mode0, 2 = mode1, 3 = mode2, 4 = baco, 5 = pci)