drm/panel: nt36523: Add DCS backlight support

This chip supports controlling the backlight via DCS commands, on at
least some panels. Add support for doing so.

Note this may only concern the NT36523*W* variant. Nobody knows, really,
there's no docs.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Jianhua Lu <lujianhua000@gmail.com>
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230412-topic-lenovopanel-v3-2-bcf9ba4de46f@linaro.org

drivers/gpu/drm/panel/panel-novatek-nt36523.c

@@ -5,6 +5,7 @@
  * Copyright (c) 2022, 2023 Jianhua Lu <lujianhua000@gmail.com>
  */
 
+#include <linux/backlight.h>
 #include <linux/delay.h>
 #include <linux/gpio/consumer.h>
 #include <linux/module.h>
@@ -53,6 +54,7 @@ struct panel_desc {
 	int (*init_sequence)(struct panel_info *pinfo);
 
 	bool is_dual_dsi;
+	bool has_dcs_backlight;
 };
 
 static inline struct panel_info *to_panel_info(struct drm_panel *panel)
@@ -679,6 +681,59 @@ static const struct drm_panel_funcs nt36523_panel_funcs = {
 	.get_modes = nt36523_get_modes,
 };
 
+static int nt36523_bl_update_status(struct backlight_device *bl)
+{
+	struct mipi_dsi_device *dsi = bl_get_data(bl);
+	u16 brightness = backlight_get_brightness(bl);
+	int ret;
+
+	dsi->mode_flags &= ~MIPI_DSI_MODE_LPM;
+
+	ret = mipi_dsi_dcs_set_display_brightness_large(dsi, brightness);
+	if (ret < 0)
+		return ret;
+
+	dsi->mode_flags |= MIPI_DSI_MODE_LPM;
+
+	return 0;
+}
+
+static int nt36523_bl_get_brightness(struct backlight_device *bl)
+{
+	struct mipi_dsi_device *dsi = bl_get_data(bl);
+	u16 brightness;
+	int ret;
+
+	dsi->mode_flags &= ~MIPI_DSI_MODE_LPM;
+
+	ret = mipi_dsi_dcs_get_display_brightness_large(dsi, &brightness);
+	if (ret < 0)
+		return ret;
+
+	dsi->mode_flags |= MIPI_DSI_MODE_LPM;
+
+	return brightness;
+}
+
+static const struct backlight_ops nt36523_bl_ops = {
+	.update_status = nt36523_bl_update_status,
+	.get_brightness = nt36523_bl_get_brightness,
+};
+
+static struct backlight_device *nt36523_create_backlight(struct mipi_dsi_device *dsi)
+{
+	struct device *dev = &dsi->dev;
+	const struct backlight_properties props = {
+		.type = BACKLIGHT_RAW,
+		.brightness = 512,
+		.max_brightness = 4095,
+		.scale = BACKLIGHT_SCALE_NON_LINEAR,
+	};
+
+	return devm_backlight_device_register(dev, dev_name(dev), dev, dsi,
+					      &nt36523_bl_ops, &props);
+}
+
 static int nt36523_probe(struct mipi_dsi_device *dsi)
 {
 	struct device *dev = &dsi->dev;
@@ -730,9 +785,16 @@ static int nt36523_probe(struct mipi_dsi_device *dsi)
 	mipi_dsi_set_drvdata(dsi, pinfo);
 	drm_panel_init(&pinfo->panel, dev, &nt36523_panel_funcs, DRM_MODE_CONNECTOR_DSI);
 
-	ret = drm_panel_of_backlight(&pinfo->panel);
-	if (ret)
-		return dev_err_probe(dev, ret, "failed to get backlight\n");
+	if (pinfo->desc->has_dcs_backlight) {
+		pinfo->panel.backlight = nt36523_create_backlight(dsi);
+		if (IS_ERR(pinfo->panel.backlight))
+			return dev_err_probe(dev, PTR_ERR(pinfo->panel.backlight),
+					     "Failed to create backlight\n");
+	} else {
+		ret = drm_panel_of_backlight(&pinfo->panel);
+		if (ret)
+			return dev_err_probe(dev, ret, "Failed to get backlight\n");
+	}
 
 	drm_panel_add(&pinfo->panel);