[RFC PATCH 04/10] drm/panel_helper: Introduce drm_panel_helper

[Douglas Anderson <dianders@chromium.org>]

The goal of this file is to contain helper functions for panel drivers
to use. To start off with, let's add drm_panel_helper_shutdown() for
use by panels that want to make sure they're powered off at
shutdown/remove time if they happen to be powered on.

The main goal of introducting this function is so that panel drivers
don't need to track the enabled/prepared state themselves.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
If I've misunderstood and the drm_panel_helper_shutdown() should
belong in some other file and we don't need to introduce a "helper"
for this then please le me know.

 drivers/gpu/drm/Makefile           |  1 +
 drivers/gpu/drm/drm_panel_helper.c | 37 ++++++++++++++++++++++++++++++
 include/drm/drm_panel_helper.h     | 13 +++++++++++
 3 files changed, 51 insertions(+)
 create mode 100644 drivers/gpu/drm/drm_panel_helper.c
 create mode 100644 include/drm/drm_panel_helper.h

diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 215e78e79125..e811f3d68235 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -118,6 +118,7 @@ drm_kms_helper-y := \
 	drm_gem_framebuffer_helper.o \
 	drm_kms_helper_common.o \
 	drm_modeset_helper.o \
+	drm_panel_helper.o \
 	drm_plane_helper.o \
 	drm_probe_helper.o \
 	drm_rect.o \
diff --git a/drivers/gpu/drm/drm_panel_helper.c b/drivers/gpu/drm/drm_panel_helper.c
new file mode 100644
index 000000000000..85a55b5731cf
--- /dev/null
+++ b/drivers/gpu/drm/drm_panel_helper.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2023 Google Inc.
+ */
+
+#include <linux/dev_printk.h>
+
+#include <drm/drm_panel.h>
+#include <drm/drm_panel_helper.h>
+
+/**
+ * drm_panel_helper_shutdown - helper for panels to use at shutdown time
+ * @panel: DRM panel
+ *
+ * Panels may call this function unconditionally at shutdown time to ensure
+ * that they are disabled and unprepared if necessary.
+ *
+ * As part of this function:
+ * - The backlight will be turned off, if it was on.
+ * - Any panel followers will be power sequenced.
+ */
+void drm_panel_helper_shutdown(struct drm_panel *panel)
+{
+	int ret;
+
+	if (panel->enabled) {
+		ret = drm_panel_disable(panel);
+		if (ret)
+			dev_warn(panel->dev, "Error disabling panel %d\n", ret);
+	}
+	if (panel->prepared) {
+		ret = drm_panel_unprepare(panel);
+		if (ret)
+			dev_warn(panel->dev, "Error unpreparing panel %d\n", ret);
+	}
+}
+EXPORT_SYMBOL_GPL(drm_panel_helper_shutdown);
diff --git a/include/drm/drm_panel_helper.h b/include/drm/drm_panel_helper.h
new file mode 100644
index 000000000000..5621482053a9
--- /dev/null
+++ b/include/drm/drm_panel_helper.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright 2023 Google Inc.
+ */
+
+#ifndef DRM_PANEL_HELPER_H
+#define DRM_PANEL_HELPER_H
+
+struct drm_panel;
+
+void drm_panel_helper_shutdown(struct drm_panel *panel);
+
+#endif /* DRM_PANEL_HELPER_H */
-- 
2.41.0.585.gd2178a4bd4-goog