drm/radeon/dpm: implement vblank_too_short callback for 7xx

Check if we can switch the mclk during the vblank time otherwise
we may get artifacts on the screen when the mclk changes.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_asic.c

@@ -1394,6 +1394,7 @@ static struct radeon_asic rv770_asic = {
 		.print_power_state = &rv770_dpm_print_power_state,
 		.debugfs_print_current_performance_level = &rv770_dpm_debugfs_print_current_performance_level,
 		.force_performance_level = &rv770_dpm_force_performance_level,
+		.vblank_too_short = &rv770_dpm_vblank_too_short,
 	},
 	.pflip = {
 		.pre_page_flip = &rs600_pre_page_flip,

drivers/gpu/drm/radeon/radeon_asic.h

@@ -480,6 +480,7 @@ void rv770_dpm_debugfs_print_current_performance_level(struct radeon_device *rde
 						       struct seq_file *m);
 int rv770_dpm_force_performance_level(struct radeon_device *rdev,
 				      enum radeon_dpm_forced_level level);
+bool rv770_dpm_vblank_too_short(struct radeon_device *rdev);
 
 /*
  * evergreen

drivers/gpu/drm/radeon/rv770_dpm.c

@@ -2508,3 +2508,14 @@ u32 rv770_dpm_get_mclk(struct radeon_device *rdev, bool low)
 	else
 		return requested_state->high.mclk;
 }
+
+bool rv770_dpm_vblank_too_short(struct radeon_device *rdev)
+{
+	u32 vblank_time = r600_dpm_get_vblank_time(rdev);
+
+	if (vblank_time < 300)
+		return true;
+	else
+		return false;
+
+}