drm/radeon/dpm: implement vblank_too_short callback for evergreen

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/cypress_dpm.c

@@ -2174,3 +2174,16 @@ void cypress_dpm_fini(struct radeon_device *rdev)
 	kfree(rdev->pm.dpm.ps);
 	kfree(rdev->pm.dpm.priv);
 }
+
+bool cypress_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;
+
+}

drivers/gpu/drm/radeon/radeon_asic.c

@@ -1519,6 +1519,7 @@ static struct radeon_asic evergreen_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 = &cypress_dpm_vblank_too_short,
 	},
 	.pflip = {
 		.pre_page_flip = &evergreen_pre_page_flip,

drivers/gpu/drm/radeon/radeon_asic.h

@@ -545,6 +545,7 @@ void cypress_dpm_disable(struct radeon_device *rdev);
 int cypress_dpm_set_power_state(struct radeon_device *rdev);
 void cypress_dpm_display_configuration_changed(struct radeon_device *rdev);
 void cypress_dpm_fini(struct radeon_device *rdev);
+bool cypress_dpm_vblank_too_short(struct radeon_device *rdev);
 int btc_dpm_init(struct radeon_device *rdev);
 void btc_dpm_setup_asic(struct radeon_device *rdev);
 int btc_dpm_enable(struct radeon_device *rdev);