drm/amd/display: Look at firmware version to determine using dmub on dcn21

commit 652de07add ("drm/amd/display: Fully switch to dmub for all dcn21
asics") switched over to using dmub on Renoir to fix Gitlab 1735, but this
implied a new dependency on newer firmware which might not be met on older
kernel versions.

Since sw_init runs before hw_init, there is an opportunity to determine
whether or not the firmware version is new to adjust the behavior.

Cc: Roman.Li@amd.com
BugLink: https://gitlab.freedesktop.org/drm/amd/-/issues/1772
BugLink: https://gitlab.freedesktop.org/drm/amd/-/issues/1735
Fixes: 652de07add ("drm/amd/display: Fully switch to dmub for all dcn21 asics")
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Roman Li <Roman.Li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1410,7 +1410,15 @@ static int amdgpu_dm_init(struct amdgpu_device *adev)
 		switch (adev->ip_versions[DCE_HWIP][0]) {
 		case IP_VERSION(2, 1, 0):
 			init_data.flags.gpu_vm_support = true;
-			init_data.flags.disable_dmcu = true;
+			switch (adev->dm.dmcub_fw_version) {
+			case 0: /* development */
+			case 0x1: /* linux-firmware.git hash 6d9f399 */
+			case 0x01000000: /* linux-firmware.git hash 9a0b0f4 */
+				init_data.flags.disable_dmcu = false;
+				break;
+			default:
+				init_data.flags.disable_dmcu = true;
+			}
 			break;
 		case IP_VERSION(1, 0, 0):
 		case IP_VERSION(1, 0, 1):