Re: [PATCH 4/4] drm/panel: himax-hx83102: Add support for DSI DCS backlight control

[Neil Armstrong <neil.armstrong@linaro.org>]

On 2/17/26 08:00, Val Packett wrote:
> The HTF065H045 panel based on the HX83102 controller does use DCS
> commands for controlling backlight brightness. Make the driver fall back
> to DCS when no external backlight has been defined in the device tree,
> like many other drivers do.
> 
> Signed-off-by: Val Packett <val@packett.cool>
> ---
>   drivers/gpu/drm/panel/panel-himax-hx83102.c | 65 +++++++++++++++++++++
>   1 file changed, 65 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panel/panel-himax-hx83102.c b/drivers/gpu/drm/panel/panel-himax-hx83102.c
> index 34e0e956db48..8b2a68ee851e 100644
> --- a/drivers/gpu/drm/panel/panel-himax-hx83102.c
> +++ b/drivers/gpu/drm/panel/panel-himax-hx83102.c
> @@ -7,6 +7,7 @@
>    * Based on drivers/gpu/drm/panel/panel-himax-hx8394.c
>    */
>   
> +#include <linux/backlight.h>
>   #include <linux/delay.h>
>   #include <linux/gpio/consumer.h>
>   #include <linux/module.h>
> @@ -76,6 +77,8 @@ struct hx83102_panel_desc {
>   		unsigned int height_mm;
>   	} size;
>   
> +	bool has_backlight;
> +
>   	int (*init)(struct hx83102 *ctx);
>   };
>   
> @@ -913,6 +916,7 @@ static const struct hx83102_panel_desc holitech_htf065h045_desc = {
>   		.width_mm = 68,
>   		.height_mm = 151,
>   	},
> +	.has_backlight = true,
>   	.init = holitech_htf065h045_init,
>   };
>   
> @@ -1049,6 +1053,59 @@ static const struct drm_panel_funcs hx83102_drm_funcs = {
>   	.get_orientation = hx83102_get_orientation,
>   };
>   
> +static int hx83102_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 hx83102_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 hx83102_bl_ops = {
> +	.update_status = hx83102_bl_update_status,
> +	.get_brightness = hx83102_bl_get_brightness,
> +};
> +
> +static struct backlight_device *
> +hx83102_create_dcs_backlight(struct mipi_dsi_device *dsi)
> +{
> +	struct device *dev = &dsi->dev;
> +	const struct backlight_properties props = {
> +		.type = BACKLIGHT_RAW,
> +		.brightness = 4095,
> +		.max_brightness = 4095,

I guess those values could be in the hx83102_panel_desc.

Anyway:

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>

Thanks,
Neil

> +	};
> +
> +	return devm_backlight_device_register(dev, dev_name(dev), dev, dsi,
> +					      &hx83102_bl_ops, &props);
> +}
> +
>   static int hx83102_panel_add(struct hx83102 *ctx)
>   {
>   	struct device *dev = &ctx->dsi->dev;
> @@ -1080,6 +1137,14 @@ static int hx83102_panel_add(struct hx83102 *ctx)
>   	if (err)
>   		return err;
>   
> +	/* Use DSI-based backlight as fallback if available */
> +	if (ctx->desc->has_backlight && !ctx->base.backlight) {
> +		ctx->base.backlight = hx83102_create_dcs_backlight(ctx->dsi);
> +		if (IS_ERR(ctx->base.backlight))
> +			return dev_err_probe(dev, PTR_ERR(ctx->base.backlight),
> +					     "Failed to create backlight\n");
> +	}
> +
>   	ctx->base.funcs = &hx83102_drm_funcs;
>   	ctx->base.dev = &ctx->dsi->dev;
>