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.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
---
 drivers/gpu/drm/panel/panel-novatek-nt36523.c | 67 +++++++++++++++++++++++++--
 1 file changed, 64 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-novatek-nt36523.c b/drivers/gpu/drm/panel/panel-novatek-nt36523.c
index d30dbbfb67b1..3c81ec014eef 100644
--- a/drivers/gpu/drm/panel/panel-novatek-nt36523.c
+++ b/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 +681,58 @@ 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,
+	};
+
+	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 +784,16 @@ 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);
 

-- 
2.40.0

On Wed, Apr 12, 2023 at 9:46 PM Konrad Dybcio <konrad.dybcio@linaro.org> wrote:

> 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.
>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

On Wed, Apr 12, 2023 at 09:46:00PM +0200, Konrad Dybcio wrote:
> 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.
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
> ---
>  drivers/gpu/drm/panel/panel-novatek-nt36523.c | 67 +++++++++++++++++++++++++--
>  1 file changed, 64 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-novatek-nt36523.c b/drivers/gpu/drm/panel/panel-novatek-nt36523.c
> index d30dbbfb67b1..3c81ec014eef 100644
> --- a/drivers/gpu/drm/panel/panel-novatek-nt36523.c
> +++ b/drivers/gpu/drm/panel/panel-novatek-nt36523.c
> @@ -5,6 +5,7 @@
>   * Copyright (c) 2022, 2023 Jianhua Lu <lujianhua000@gmail.com>
>   */
>  
> +
[..]
> +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,
Please set the missing scale property of backlight. Daniel said: "Unknown is never correct for
new drivers."
See https://lore.kernel.org/lkml/Y6SIWoVFX%2FOlNO0n@aspen.lan/

Otherwise,

Reviewed-by: Jianhua Lu <lujianhua000@gmail.com>
> +	};
> +
> +	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 +784,16 @@ 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);
>  
> 
> -- 
> 2.40.0
>