linux-kernel - RE: [PATCH 1/2] drm/dp: Add drm_edp_backlight_get

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Message-ID: <DM3PPF208195D8D72521EAAFDA64C84654FE31EA@DM3PPF208195D8D.namprd11.prod.outlook.com>
Date: Fri, 26 Sep 2025 09:23:39 +0000
From: "Kandpal, Suraj" <suraj.kandpal@...el.com>
To: "Aaron, Ma" <aaron.ma@...onical.com>, "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>, "intel-gfx@...ts.freedesktop.org"
	<intel-gfx@...ts.freedesktop.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
	"mripard@...nel.org" <mripard@...nel.org>, "tzimmermann@...e.de"
	<tzimmermann@...e.de>, "airlied@...il.com" <airlied@...il.com>,
	"simona@...ll.ch" <simona@...ll.ch>, "jani.nikula@...ux.intel.com"
	<jani.nikula@...ux.intel.com>, "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
	"Deak, Imre" <imre.deak@...el.com>, "joonas.lahtinen@...ux.intel.com"
	<joonas.lahtinen@...ux.intel.com>, "Aaron, Ma" <aaron.ma@...onical.com>
Subject: RE: [PATCH 1/2] drm/dp: Add drm_edp_backlight_get_level

> Subject: [PATCH 1/2] drm/dp: Add drm_edp_backlight_get_level
> 
> Implement drm_edp_backlight_get_level() to read the current backlight
> brightness level from eDP DPCD registers via AUX channel.
> 
> Signed-off-by: Aaron Ma <aaron.ma@...onical.com>
> ---
>  drivers/gpu/drm/display/drm_dp_helper.c | 52 +++++++++++++++++++++++++
>  include/drm/display/drm_dp_helper.h     |  1 +
>  2 files changed, 53 insertions(+)
> 
> diff --git a/drivers/gpu/drm/display/drm_dp_helper.c
> b/drivers/gpu/drm/display/drm_dp_helper.c
> index 1ecc3df7e3167..0cfb357ebd9e2 100644
> --- a/drivers/gpu/drm/display/drm_dp_helper.c
> +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> @@ -3945,6 +3945,58 @@ int drm_dp_pcon_convert_rgb_to_ycbcr(struct
> drm_dp_aux *aux, u8 color_spc)  }
> EXPORT_SYMBOL(drm_dp_pcon_convert_rgb_to_ycbcr);
> 
> +/**
> + * drm_edp_backlight_get_level - Get the backlight level of eDP DPCD
> +via AUX
> + * @aux: The DP aux device
> + * @bl: Backlight capability info from the panel
> + *
> + * Reads the current backlight brightness level from luminance mode
> + * (24-bit value in nits) or DPCD AUX mode(16-bit and 8-bit modes).
> + *
> + * Returns: Current backlight level.
> + */
> +u32 drm_edp_backlight_get_level(struct drm_dp_aux *aux, const struct
> +drm_edp_backlight_info *bl) {
> +	int ret;
> +	u8 buf[3] = { 0 };
> +	u32 level = 0;
> +
> +	if (!(bl->aux_set || bl->luminance_set))
> +		return 0;
> +
> +	if (bl->luminance_set) {
> +		ret = drm_dp_dpcd_read(aux,
> DP_EDP_PANEL_TARGET_LUMINANCE_VALUE, buf, sizeof(buf));
> +		if (ret < 0) {
> +			DRM_DEV_ERROR(aux->drm_dev->dev,
> +				      "%s: Failed to read luminance value: %d\n",
> +				      aux->name, ret);
> +			return 0;
> +		}
> +		level = (buf[2] << 16 | buf[1] << 8 | buf[0]) / 1000;
> +	} else if (bl->lsb_reg_used) {
> +		ret = drm_dp_dpcd_read(aux,
> DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, buf, 2);
> +		if (ret < 0) {
> +			DRM_DEV_ERROR(aux->drm_dev->dev,

Use drm_err here ditto for same where ever this has been used

Regards,
Suraj Kandpal

> +				      "%s: Failed to read backlight level: %d\n",
> +				      aux->name, ret);
> +			return 0;
> +		}
> +		level = buf[0] << 8 | buf[1];
> +	} else {
> +		ret = drm_dp_dpcd_read(aux,
> DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, buf, 1);
> +		if (ret < 0) {
> +			DRM_DEV_ERROR(aux->drm_dev->dev,
> +				      "%s: Failed to read backlight level: %d\n",
> +				      aux->name, ret);
> +			return 0;
> +		}
> +		level = buf[0];
> +	}
> +
> +	return level;
> +}
> +EXPORT_SYMBOL(drm_edp_backlight_get_level);
> +
>  /**
>   * drm_edp_backlight_set_level() - Set the backlight level of an eDP panel via
> AUX
>   * @aux: The DP AUX channel to use
> diff --git a/include/drm/display/drm_dp_helper.h
> b/include/drm/display/drm_dp_helper.h
> index 87caa4f1fdb86..0b045a47ae573 100644
> --- a/include/drm/display/drm_dp_helper.h
> +++ b/include/drm/display/drm_dp_helper.h
> @@ -864,6 +864,7 @@ drm_edp_backlight_init(struct drm_dp_aux *aux,
> struct drm_edp_backlight_info *bl
>  		       u32 max_luminance,
>  		       u16 driver_pwm_freq_hz, const u8
> edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
>  		       u32 *current_level, u8 *current_mode, bool
> need_luminance);
> +u32 drm_edp_backlight_get_level(struct drm_dp_aux *aux, const struct
> +drm_edp_backlight_info *bl);
>  int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct
> drm_edp_backlight_info *bl,
>  				u32 level);
>  int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct
> drm_edp_backlight_info *bl,
> --
> 2.43.0