drm/amd/display: Add and use new dm_prepare_suspend() callback

[Why]
The displays currently don't get turned off until after other IP blocks
have been suspended.  However turning off the displays first gives a
very visible response that the system is on it's way down.

[How]
Turn off displays in a prepare_suspend() callback instead when possible.
This will help for suspend and hibernate sequences.
The shutdown sequence however will not call prepare() so check whether
the state has been already saved to decide what to do.

Acked-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: superm1

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

@@ -3141,6 +3141,21 @@ static void hpd_rx_irq_work_suspend(struct amdgpu_display_manager *dm)
 	}
 }
 
+static int dm_prepare_suspend(struct amdgpu_ip_block *ip_block)
+{
+	struct amdgpu_device *adev = ip_block->adev;
+
+	if (amdgpu_in_reset(adev))
+		return 0;
+
+	WARN_ON(adev->dm.cached_state);
+	adev->dm.cached_state = drm_atomic_helper_suspend(adev_to_drm(adev));
+	if (IS_ERR(adev->dm.cached_state))
+		return PTR_ERR(adev->dm.cached_state);
+
+	return 0;
+}
+
 static int dm_suspend(struct amdgpu_ip_block *ip_block)
 {
 	struct amdgpu_device *adev = ip_block->adev;
@@ -3171,10 +3186,11 @@ static int dm_suspend(struct amdgpu_ip_block *ip_block)
 		return 0;
 	}
 
-	WARN_ON(adev->dm.cached_state);
-	adev->dm.cached_state = drm_atomic_helper_suspend(adev_to_drm(adev));
-	if (IS_ERR(adev->dm.cached_state))
-		return PTR_ERR(adev->dm.cached_state);
+	if (!adev->dm.cached_state) {
+		adev->dm.cached_state = drm_atomic_helper_suspend(adev_to_drm(adev));
+		if (IS_ERR(adev->dm.cached_state))
+			return PTR_ERR(adev->dm.cached_state);
+	}
 
 	s3_handle_hdmi_cec(adev_to_drm(adev), true);
 
@@ -3606,6 +3622,7 @@ static const struct amd_ip_funcs amdgpu_dm_funcs = {
 	.early_fini = amdgpu_dm_early_fini,
 	.hw_init = dm_hw_init,
 	.hw_fini = dm_hw_fini,
+	.prepare_suspend = dm_prepare_suspend,
 	.suspend = dm_suspend,
 	.resume = dm_resume,
 	.is_idle = dm_is_idle,