drm/radeon/dpm: implement vblank_too_short callback for cayman

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/ni_dpm.c

@@ -765,6 +765,19 @@ static void ni_calculate_leakage_for_v_and_t(struct radeon_device *rdev,
 	ni_calculate_leakage_for_v_and_t_formula(coeff, v, t, i_leakage, leakage);
 }
 
+bool ni_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 : 300;
+
+	if (vblank_time < switch_limit)
+		return true;
+	else
+		return false;
+
+}
+
 static void ni_apply_state_adjust_rules(struct radeon_device *rdev,
 					struct radeon_ps *rps)
 {
@@ -775,7 +788,8 @@ static void ni_apply_state_adjust_rules(struct radeon_device *rdev,
 	u16 vddc, vddci;
 	int i;
 
-	if (rdev->pm.dpm.new_active_crtc_count > 1)
+	if ((rdev->pm.dpm.new_active_crtc_count > 1) ||
+	    ni_dpm_vblank_too_short(rdev))
 		disable_mclk_switching = true;
 	else
 		disable_mclk_switching = false;

drivers/gpu/drm/radeon/radeon_asic.c

@@ -1945,6 +1945,7 @@ static struct radeon_asic cayman_asic = {
 		.print_power_state = &ni_dpm_print_power_state,
 		.debugfs_print_current_performance_level = &ni_dpm_debugfs_print_current_performance_level,
 		.force_performance_level = &ni_dpm_force_performance_level,
+		.vblank_too_short = &ni_dpm_vblank_too_short,
 	},
 	.pflip = {
 		.pre_page_flip = &evergreen_pre_page_flip,

drivers/gpu/drm/radeon/radeon_asic.h

@@ -624,6 +624,7 @@ void ni_dpm_debugfs_print_current_performance_level(struct radeon_device *rdev,
 						    struct seq_file *m);
 int ni_dpm_force_performance_level(struct radeon_device *rdev,
 				   enum radeon_dpm_forced_level level);
+bool ni_dpm_vblank_too_short(struct radeon_device *rdev);
 int trinity_dpm_init(struct radeon_device *rdev);
 int trinity_dpm_enable(struct radeon_device *rdev);
 void trinity_dpm_disable(struct radeon_device *rdev);