drm/imx/dcss: Call drm_atomic_helper_shutdown() at shutdown time

Based on grepping through the source code this driver appears to be
missing a call to drm_atomic_helper_shutdown() at system shutdown
time. Among other things, this means that if a panel is in use that it
won't be cleanly powered off at system shutdown time.

The fact that we should call drm_atomic_helper_shutdown() in the case
of OS shutdown/restart comes straight out of the kernel doc "driver
instance overview" in drm_drv.c.
Suggested-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Tested-by: Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>
Reviewed-by: Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230921122641.RFT.v2.1.I134336fce7eac5a63bdac46d57b0888858fc8081@changeid

drivers/gpu/drm/imx/dcss/dcss-drv.c

@@ -92,6 +92,13 @@ static int dcss_drv_platform_remove(struct platform_device *pdev)
 	return 0;
 }
 
+static void dcss_drv_platform_shutdown(struct platform_device *pdev)
+{
+	struct dcss_drv *mdrv = dev_get_drvdata(&pdev->dev);
+
+	dcss_kms_shutdown(mdrv->kms);
+}
+
 static struct dcss_type_data dcss_types[] = {
 	[DCSS_IMX8MQ] = {
 		.name = "DCSS_IMX8MQ",
@@ -114,6 +121,7 @@ MODULE_DEVICE_TABLE(of, dcss_of_match);
 static struct platform_driver dcss_platform_driver = {
 	.probe	= dcss_drv_platform_probe,
 	.remove	= dcss_drv_platform_remove,
+	.shutdown = dcss_drv_platform_shutdown,
 	.driver	= {
 		.name = "imx-dcss",
 		.of_match_table	= dcss_of_match,

drivers/gpu/drm/imx/dcss/dcss-kms.c

@@ -172,3 +172,10 @@ void dcss_kms_detach(struct dcss_kms_dev *kms)
 	dcss_crtc_deinit(&kms->crtc, drm);
 	drm->dev_private = NULL;
 }
+
+void dcss_kms_shutdown(struct dcss_kms_dev *kms)
+{
+	struct drm_device *drm = &kms->base;
+
+	drm_atomic_helper_shutdown(drm);
+}

drivers/gpu/drm/imx/dcss/dcss-kms.h

@@ -34,6 +34,7 @@ struct dcss_kms_dev {
 
 struct dcss_kms_dev *dcss_kms_attach(struct dcss_dev *dcss);
 void dcss_kms_detach(struct dcss_kms_dev *kms);
+void dcss_kms_shutdown(struct dcss_kms_dev *kms);
 int dcss_crtc_init(struct dcss_crtc *crtc, struct drm_device *drm);
 void dcss_crtc_deinit(struct dcss_crtc *crtc, struct drm_device *drm);
 struct dcss_plane *dcss_plane_init(struct drm_device *drm,