[PATCH v2 1/2] drm/dp: Add drm_edp_backlight_get_level

[PATCH v2 1/2] drm/dp: Add drm_edp_backlight_get_level

[Aaron Ma]

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@canonical.com>
---
v1 -> v2: Use drm_err.

 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..16da5df805aa5 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_err(aux->drm_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_err(aux->drm_dev,
+				      "%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_err(aux->drm_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

[PATCH v2 2/2] drm/i915/backlight: Add get brightness support of DPCD via AUX

[Aaron Ma]

Use drm common helper to read brightness from
both luminance and AUX mode to support get_brightness from
DPCD via AUX.

Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
---
v1 -> v2: no changes.

 .../drm/i915/display/intel_dp_aux_backlight.c | 20 ++++++-------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
index 0a3a3f6a5f9d8..0ee6fd0f41ef0 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -454,24 +454,16 @@ static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector *connector, en
 {
 	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
 	struct intel_panel *panel = &connector->panel;
-	u8 buf[3];
-	u32 val = 0;
-	int ret;
 
-	if (panel->backlight.edp.vesa.luminance_control_support) {
-		ret = drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_PANEL_TARGET_LUMINANCE_VALUE, buf,
-				       sizeof(buf));
-		if (ret < 0) {
-			drm_err(intel_dp->aux.drm_dev,
-				"[CONNECTOR:%d:%s] Failed to read Luminance from DPCD\n",
-				connector->base.base.id, connector->base.name);
-			return 0;
-		}
+	if (!panel->backlight.edp.vesa.info.aux_set) {
+		u32 pwm_level = panel->backlight.pwm_funcs->get(connector, unused);
 
-		val |= buf[0] | buf[1] << 8 | buf[2] << 16;
-		return val / 1000;
+		return intel_backlight_level_from_pwm(connector, pwm_level);
 	}
 
+	connector->panel.backlight.level =
+		drm_edp_backlight_get_level(&intel_dp->aux, &panel->backlight.edp.vesa.info);
+
 	return connector->panel.backlight.level;
 }
 
-- 
2.43.0

RE: [PATCH v2 2/2] drm/i915/backlight: Add get brightness support of DPCD via AUX

[Kandpal, Suraj]

> Subject: [PATCH v2 2/2] drm/i915/backlight: Add get brightness support of
> DPCD via AUX
> 
> Use drm common helper to read brightness from both luminance and AUX
> mode to support get_brightness from DPCD via AUX.
> 

The version changes need to be here

Like this 

--v2
<change done>

Do not send revisions this quickly wait for a day or two before sending a new version since
Everyone isn't in the same time zone or could have simply missed your mail.

> Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
> ---
> v1 -> v2: no changes.

Aso this shouldn't be here
This should be above your signed-off-by
> 
>  .../drm/i915/display/intel_dp_aux_backlight.c | 20 ++++++-------------
>  1 file changed, 6 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> index 0a3a3f6a5f9d8..0ee6fd0f41ef0 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -454,24 +454,16 @@ static u32 intel_dp_aux_vesa_get_backlight(struct
> intel_connector *connector, en  {
>  	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
>  	struct intel_panel *panel = &connector->panel;
> -	u8 buf[3];
> -	u32 val = 0;
> -	int ret;
> 
> -	if (panel->backlight.edp.vesa.luminance_control_support) {
> -		ret = drm_dp_dpcd_read(&intel_dp->aux,
> DP_EDP_PANEL_TARGET_LUMINANCE_VALUE, buf,
> -				       sizeof(buf));
> -		if (ret < 0) {
> -			drm_err(intel_dp->aux.drm_dev,
> -				"[CONNECTOR:%d:%s] Failed to read
> Luminance from DPCD\n",
> -				connector->base.base.id, connector-
> >base.name);
> -			return 0;
> -		}
> +	if (!panel->backlight.edp.vesa.info.aux_set) {
> +		u32 pwm_level = panel->backlight.pwm_funcs->get(connector,
> unused);
> 
> -		val |= buf[0] | buf[1] << 8 | buf[2] << 16;
> -		return val / 1000;
> +		return intel_backlight_level_from_pwm(connector,
> pwm_level);
>  	}
> 
> +	connector->panel.backlight.level =
> +		drm_edp_backlight_get_level(&intel_dp->aux,
> +&panel->backlight.edp.vesa.info);
> +
>  	return connector->panel.backlight.level;  }
> 
> --
> 2.43.0

Re: [PATCH v2 2/2] drm/i915/backlight: Add get brightness support of DPCD via AUX

[Aaron Ma]

On Fri, Sep 26, 2025 at 5:52 PM Kandpal, Suraj <suraj.kandpal@intel.com> wrote:
>
> > Subject: [PATCH v2 2/2] drm/i915/backlight: Add get brightness support of
> > DPCD via AUX
> >
> > Use drm common helper to read brightness from both luminance and AUX
> > mode to support get_brightness from DPCD via AUX.
> >
>
> The version changes need to be here
>
> Like this
>
> --v2
> <change done>

This version changes follow the guidance in Commentary of
Documentation/process/submitting-patches.rst


>
> Do not send revisions this quickly wait for a day or two before sending a new version since
> Everyone isn't in the same time zone or could have simply missed your mail.
>

I found the drm_err once the email sent out. so I made this change.

Aaron


> > Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
> > ---
> > v1 -> v2: no changes.
>
> Aso this shouldn't be here
> This should be above your signed-off-by
> >
> >  .../drm/i915/display/intel_dp_aux_backlight.c | 20 ++++++-------------
> >  1 file changed, 6 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > index 0a3a3f6a5f9d8..0ee6fd0f41ef0 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > @@ -454,24 +454,16 @@ static u32 intel_dp_aux_vesa_get_backlight(struct
> > intel_connector *connector, en  {
> >       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> >       struct intel_panel *panel = &connector->panel;
> > -     u8 buf[3];
> > -     u32 val = 0;
> > -     int ret;
> >
> > -     if (panel->backlight.edp.vesa.luminance_control_support) {
> > -             ret = drm_dp_dpcd_read(&intel_dp->aux,
> > DP_EDP_PANEL_TARGET_LUMINANCE_VALUE, buf,
> > -                                    sizeof(buf));
> > -             if (ret < 0) {
> > -                     drm_err(intel_dp->aux.drm_dev,
> > -                             "[CONNECTOR:%d:%s] Failed to read
> > Luminance from DPCD\n",
> > -                             connector->base.base.id, connector-
> > >base.name);
> > -                     return 0;
> > -             }
> > +     if (!panel->backlight.edp.vesa.info.aux_set) {
> > +             u32 pwm_level = panel->backlight.pwm_funcs->get(connector,
> > unused);
> >
> > -             val |= buf[0] | buf[1] << 8 | buf[2] << 16;
> > -             return val / 1000;
> > +             return intel_backlight_level_from_pwm(connector,
> > pwm_level);
> >       }
> >
> > +     connector->panel.backlight.level =
> > +             drm_edp_backlight_get_level(&intel_dp->aux,
> > +&panel->backlight.edp.vesa.info);
> > +
> >       return connector->panel.backlight.level;  }
> >
> > --
> > 2.43.0
>

RE: [PATCH v2 1/2] drm/dp: Add drm_edp_backlight_get_level

[Kandpal, Suraj]

> Subject: [PATCH v2 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.

Versioning info should have been here
Like this 
--v2
<Changes Done>

With that fixed LGTM,
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>

> 
> Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
> ---
> v1 -> v2: Use drm_err.
> 
>  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..16da5df805aa5 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_err(aux->drm_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_err(aux->drm_dev,
> +				      "%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_err(aux->drm_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