drm/radeon/dpm: implement vblank_too_short callback for btc

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/btc_dpm.c

@@ -2059,6 +2059,19 @@ static void btc_init_stutter_mode(struct radeon_device *rdev)
 	}
 }
 
+bool btc_dpm_vblank_too_short(struct radeon_device *rdev)
+{
+	struct rv7xx_power_info *pi = rv770_get_pi(rdev);
+	u32 vblank_time = r600_dpm_get_vblank_time(rdev);
+	u32 switch_limit = pi->mem_gddr5 ? 450 : 100;
+
+	if (vblank_time < switch_limit)
+		return true;
+	else
+		return false;
+
+}
+
 static void btc_apply_state_adjust_rules(struct radeon_device *rdev,
 					 struct radeon_ps *rps)
 {
@@ -2068,7 +2081,8 @@ static void btc_apply_state_adjust_rules(struct radeon_device *rdev,
 	u32 mclk, sclk;
 	u16 vddc, vddci;
 
-	if (rdev->pm.dpm.new_active_crtc_count > 1)
+	if ((rdev->pm.dpm.new_active_crtc_count > 1) ||
+	    btc_dpm_vblank_too_short(rdev))
 		disable_mclk_switching = true;
 	else
 		disable_mclk_switching = false;

drivers/gpu/drm/radeon/radeon_asic.c

@@ -1768,6 +1768,7 @@ static struct radeon_asic btc_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 = &btc_dpm_vblank_too_short,
 	},
 	.pflip = {
 		.pre_page_flip = &evergreen_pre_page_flip,

drivers/gpu/drm/radeon/radeon_asic.h

@@ -556,6 +556,7 @@ void btc_dpm_post_set_power_state(struct radeon_device *rdev);
 void btc_dpm_fini(struct radeon_device *rdev);
 u32 btc_dpm_get_sclk(struct radeon_device *rdev, bool low);
 u32 btc_dpm_get_mclk(struct radeon_device *rdev, bool low);
+bool btc_dpm_vblank_too_short(struct radeon_device *rdev);
 int sumo_dpm_init(struct radeon_device *rdev);
 int sumo_dpm_enable(struct radeon_device *rdev);
 void sumo_dpm_disable(struct radeon_device *rdev);