diff mbox series

[v8,1/6] drm/panel: add basic DP AUX backlight support

Message ID 1624726268-14869-2-git-send-email-rajeevny@codeaurora.org (mailing list archive)
State New, archived
Headers show
Series drm: Support basic DPCD backlight in panel-simple and add a new panel ATNA33XC20 | expand

Commit Message

Rajeev Nandan June 26, 2021, 4:51 p.m. UTC 
Some panels support backlight control over DP AUX channel using
VESA's standard backlight control interface.
Using new DRM eDP backlight helpers, add support to create and
register a backlight for those panels in drm_panel to simplify
the panel drivers.

The panel driver with access to "struct drm_dp_aux" can create and
register a backlight device using following code snippet in its
probe() function:

	err = drm_panel_dp_aux_backlight(panel, aux);
	if (err)
		return err;

Then drm_panel will handle backlight_(enable|disable) calls
similar to the case when drm_panel_of_backlight() is used.

Currently, we are not supporting one feature where the source
device can combine the backlight brightness levels set through
DP AUX and the BL_PWM_DIM eDP connector pin. Since it's not
required for the basic backlight controls, it can be added later.

Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Lyude Paul <lyude@redhat.com>
---

Changes in v5:
- New

Changes in v6:
- Fixed ordering of memory allocation (Douglas)
- Updated word wrapping in a comment (Douglas)

Changes in v8:
- Now using backlight_is_blank() to get the backlight blank status (Sam Ravnborg)

 drivers/gpu/drm/drm_panel.c | 108 ++++++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_panel.h     |  15 ++++--
 2 files changed, 119 insertions(+), 4 deletions(-)

Comments

Thomas Zimmermann July 12, 2021, 9:41 a.m. UTC | #1 
Am 26.06.21 um 18:51 schrieb Rajeev Nandan:
> Some panels support backlight control over DP AUX channel using
> VESA's standard backlight control interface.
> Using new DRM eDP backlight helpers, add support to create and
> register a backlight for those panels in drm_panel to simplify
> the panel drivers.
> 
> The panel driver with access to "struct drm_dp_aux" can create and
> register a backlight device using following code snippet in its
> probe() function:
> 
> 	err = drm_panel_dp_aux_backlight(panel, aux);
> 	if (err)
> 		return err;
> 
> Then drm_panel will handle backlight_(enable|disable) calls
> similar to the case when drm_panel_of_backlight() is used.
> 
> Currently, we are not supporting one feature where the source
> device can combine the backlight brightness levels set through
> DP AUX and the BL_PWM_DIM eDP connector pin. Since it's not
> required for the basic backlight controls, it can be added later.
> 
> Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
> Reviewed-by: Douglas Anderson <dianders@chromium.org>
> Reviewed-by: Lyude Paul <lyude@redhat.com>
> ---
> 
> Changes in v5:
> - New
> 
> Changes in v6:
> - Fixed ordering of memory allocation (Douglas)
> - Updated word wrapping in a comment (Douglas)
> 
> Changes in v8:
> - Now using backlight_is_blank() to get the backlight blank status (Sam Ravnborg)
> 
>   drivers/gpu/drm/drm_panel.c | 108 ++++++++++++++++++++++++++++++++++++++++++++
>   include/drm/drm_panel.h     |  15 ++++--
>   2 files changed, 119 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index f634371..4fa1e3b 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -26,12 +26,20 @@
>   #include <linux/module.h>
>   
>   #include <drm/drm_crtc.h>
> +#include <drm/drm_dp_helper.h>
>   #include <drm/drm_panel.h>
>   #include <drm/drm_print.h>
>   
>   static DEFINE_MUTEX(panel_lock);
>   static LIST_HEAD(panel_list);
>   
> +struct dp_aux_backlight {
> +	struct backlight_device *base;
> +	struct drm_dp_aux *aux;
> +	struct drm_edp_backlight_info info;
> +	bool enabled;
> +};
> +
>   /**
>    * DOC: drm panel
>    *
> @@ -342,6 +350,106 @@ int drm_panel_of_backlight(struct drm_panel *panel)
>   	return 0;
>   }
>   EXPORT_SYMBOL(drm_panel_of_backlight);
> +
> +static int dp_aux_backlight_update_status(struct backlight_device *bd)
> +{
> +	struct dp_aux_backlight *bl = bl_get_data(bd);
> +	u16 brightness = backlight_get_brightness(bd);
> +	int ret = 0;
> +
> +	if (!backlight_is_blank(bd)) {
> +		if (!bl->enabled) {
> +			drm_edp_backlight_enable(bl->aux, &bl->info, brightness);
> +			bl->enabled = true;
> +			return 0;
> +		}
> +		ret = drm_edp_backlight_set_level(bl->aux, &bl->info, brightness);
> +	} else {
> +		if (bl->enabled) {
> +			drm_edp_backlight_disable(bl->aux, &bl->info);
> +			bl->enabled = false;
> +		}
> +	}
> +
> +	return ret;
> +}
> +
> +static const struct backlight_ops dp_aux_bl_ops = {
> +	.update_status = dp_aux_backlight_update_status,
> +};
> +
> +/**
> + * drm_panel_dp_aux_backlight - create and use DP AUX backlight
> + * @panel: DRM panel
> + * @aux: The DP AUX channel to use
> + *
> + * Use this function to create and handle backlight if your panel
> + * supports backlight control over DP AUX channel using DPCD
> + * registers as per VESA's standard backlight control interface.
> + *
> + * When the panel is enabled backlight will be enabled after a
> + * successful call to &drm_panel_funcs.enable()
> + *
> + * When the panel is disabled backlight will be disabled before the
> + * call to &drm_panel_funcs.disable().
> + *
> + * A typical implementation for a panel driver supporting backlight
> + * control over DP AUX will call this function at probe time.
> + * Backlight will then be handled transparently without requiring
> + * any intervention from the driver.
> + *
> + * drm_panel_dp_aux_backlight() must be called after the call to drm_panel_init().
> + *
> + * Return: 0 on success or a negative error code on failure.
> + */
> +int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux)
> +{
> +	struct dp_aux_backlight *bl;
> +	struct backlight_properties props = { 0 };
> +	u16 current_level;
> +	u8 current_mode;
> +	u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
> +	int ret;
> +
> +	if (!panel || !panel->dev || !aux)
> +		return -EINVAL;
> +
> +	ret = drm_dp_dpcd_read(aux, DP_EDP_DPCD_REV, edp_dpcd,
> +			       EDP_DISPLAY_CTL_CAP_SIZE);

This creates a cyclic dependency between drm_kms_helper-ko and drm.ko. 
drm_panel.c is in the latter, while drm_dp_dpcd_read() in 
drm_dp_helper.c is in the former. Please fix.

Best regards
Thomas

> +	if (ret < 0)
> +		return ret;
> +
> +	if (!drm_edp_backlight_supported(edp_dpcd)) {
> +		DRM_DEV_INFO(panel->dev, "DP AUX backlight is not supported\n");
> +		return 0;
> +	}
> +
> +	bl = devm_kzalloc(panel->dev, sizeof(*bl), GFP_KERNEL);
> +	if (!bl)
> +		return -ENOMEM;
> +
> +	bl->aux = aux;
> +
> +	ret = drm_edp_backlight_init(aux, &bl->info, 0, edp_dpcd,
> +				     &current_level, &current_mode);
> +	if (ret < 0)
> +		return ret;
> +
> +	props.type = BACKLIGHT_RAW;
> +	props.brightness = current_level;
> +	props.max_brightness = bl->info.max;
> +
> +	bl->base = devm_backlight_device_register(panel->dev, "dp_aux_backlight",
> +						  panel->dev, bl,
> +						  &dp_aux_bl_ops, &props);
> +	if (IS_ERR(bl->base))
> +		return PTR_ERR(bl->base);
> +
> +	panel->backlight = bl->base;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_panel_dp_aux_backlight);
>   #endif
>   
>   MODULE_AUTHOR("Thierry Reding <treding@nvidia.com>");
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 33605c3..3ebfaa6 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -32,6 +32,7 @@ struct backlight_device;
>   struct device_node;
>   struct drm_connector;
>   struct drm_device;
> +struct drm_dp_aux;
>   struct drm_panel;
>   struct display_timing;
>   
> @@ -64,8 +65,8 @@ enum drm_panel_orientation;
>    * the panel. This is the job of the .unprepare() function.
>    *
>    * Backlight can be handled automatically if configured using
> - * drm_panel_of_backlight(). Then the driver does not need to implement the
> - * functionality to enable/disable backlight.
> + * drm_panel_of_backlight() or drm_panel_dp_aux_backlight(). Then the driver
> + * does not need to implement the functionality to enable/disable backlight.
>    */
>   struct drm_panel_funcs {
>   	/**
> @@ -144,8 +145,8 @@ struct drm_panel {
>   	 * Backlight device, used to turn on backlight after the call
>   	 * to enable(), and to turn off backlight before the call to
>   	 * disable().
> -	 * backlight is set by drm_panel_of_backlight() and drivers
> -	 * shall not assign it.
> +	 * backlight is set by drm_panel_of_backlight() or
> +	 * drm_panel_dp_aux_backlight() and drivers shall not assign it.
>   	 */
>   	struct backlight_device *backlight;
>   
> @@ -208,11 +209,17 @@ static inline int of_drm_get_panel_orientation(const struct device_node *np,
>   #if IS_ENABLED(CONFIG_DRM_PANEL) && (IS_BUILTIN(CONFIG_BACKLIGHT_CLASS_DEVICE) || \
>   	(IS_MODULE(CONFIG_DRM) && IS_MODULE(CONFIG_BACKLIGHT_CLASS_DEVICE)))
>   int drm_panel_of_backlight(struct drm_panel *panel);
> +int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux);
>   #else
>   static inline int drm_panel_of_backlight(struct drm_panel *panel)
>   {
>   	return 0;
>   }
> +static inline int drm_panel_dp_aux_backlight(struct drm_panel *panel,
> +					     struct drm_dp_aux *aux)
> +{
> +	return 0;
> +}
>   #endif
>   
>   #endif
>
Thomas Zimmermann July 12, 2021, 9:45 a.m. UTC | #2 
Hi

Am 12.07.21 um 11:41 schrieb Thomas Zimmermann:
> 
> 
> Am 26.06.21 um 18:51 schrieb Rajeev Nandan:
>> Some panels support backlight control over DP AUX channel using
>> VESA's standard backlight control interface.
>> Using new DRM eDP backlight helpers, add support to create and
>> register a backlight for those panels in drm_panel to simplify
>> the panel drivers.
>>
>> The panel driver with access to "struct drm_dp_aux" can create and
>> register a backlight device using following code snippet in its
>> probe() function:
>>
>>     err = drm_panel_dp_aux_backlight(panel, aux);
>>     if (err)
>>         return err;
>>
>> Then drm_panel will handle backlight_(enable|disable) calls
>> similar to the case when drm_panel_of_backlight() is used.
>>
>> Currently, we are not supporting one feature where the source
>> device can combine the backlight brightness levels set through
>> DP AUX and the BL_PWM_DIM eDP connector pin. Since it's not
>> required for the basic backlight controls, it can be added later.
>>
>> Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
>> Reviewed-by: Douglas Anderson <dianders@chromium.org>
>> Reviewed-by: Lyude Paul <lyude@redhat.com>
>> ---
>>
>> Changes in v5:
>> - New
>>
>> Changes in v6:
>> - Fixed ordering of memory allocation (Douglas)
>> - Updated word wrapping in a comment (Douglas)
>>
>> Changes in v8:
>> - Now using backlight_is_blank() to get the backlight blank status 
>> (Sam Ravnborg)
>>
>>   drivers/gpu/drm/drm_panel.c | 108 
>> ++++++++++++++++++++++++++++++++++++++++++++
>>   include/drm/drm_panel.h     |  15 ++++--
>>   2 files changed, 119 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
>> index f634371..4fa1e3b 100644
>> --- a/drivers/gpu/drm/drm_panel.c
>> +++ b/drivers/gpu/drm/drm_panel.c
>> @@ -26,12 +26,20 @@
>>   #include <linux/module.h>
>>   #include <drm/drm_crtc.h>
>> +#include <drm/drm_dp_helper.h>
>>   #include <drm/drm_panel.h>
>>   #include <drm/drm_print.h>
>>   static DEFINE_MUTEX(panel_lock);
>>   static LIST_HEAD(panel_list);
>> +struct dp_aux_backlight {
>> +    struct backlight_device *base;
>> +    struct drm_dp_aux *aux;
>> +    struct drm_edp_backlight_info info;
>> +    bool enabled;
>> +};
>> +
>>   /**
>>    * DOC: drm panel
>>    *
>> @@ -342,6 +350,106 @@ int drm_panel_of_backlight(struct drm_panel *panel)
>>       return 0;
>>   }
>>   EXPORT_SYMBOL(drm_panel_of_backlight);
>> +
>> +static int dp_aux_backlight_update_status(struct backlight_device *bd)
>> +{
>> +    struct dp_aux_backlight *bl = bl_get_data(bd);
>> +    u16 brightness = backlight_get_brightness(bd);
>> +    int ret = 0;
>> +
>> +    if (!backlight_is_blank(bd)) {
>> +        if (!bl->enabled) {
>> +            drm_edp_backlight_enable(bl->aux, &bl->info, brightness);
>> +            bl->enabled = true;
>> +            return 0;
>> +        }
>> +        ret = drm_edp_backlight_set_level(bl->aux, &bl->info, 
>> brightness);
>> +    } else {
>> +        if (bl->enabled) {
>> +            drm_edp_backlight_disable(bl->aux, &bl->info);
>> +            bl->enabled = false;
>> +        }
>> +    }
>> +
>> +    return ret;
>> +}
>> +
>> +static const struct backlight_ops dp_aux_bl_ops = {
>> +    .update_status = dp_aux_backlight_update_status,
>> +};
>> +
>> +/**
>> + * drm_panel_dp_aux_backlight - create and use DP AUX backlight
>> + * @panel: DRM panel
>> + * @aux: The DP AUX channel to use
>> + *
>> + * Use this function to create and handle backlight if your panel
>> + * supports backlight control over DP AUX channel using DPCD
>> + * registers as per VESA's standard backlight control interface.
>> + *
>> + * When the panel is enabled backlight will be enabled after a
>> + * successful call to &drm_panel_funcs.enable()
>> + *
>> + * When the panel is disabled backlight will be disabled before the
>> + * call to &drm_panel_funcs.disable().
>> + *
>> + * A typical implementation for a panel driver supporting backlight
>> + * control over DP AUX will call this function at probe time.
>> + * Backlight will then be handled transparently without requiring
>> + * any intervention from the driver.
>> + *
>> + * drm_panel_dp_aux_backlight() must be called after the call to 
>> drm_panel_init().
>> + *
>> + * Return: 0 on success or a negative error code on failure.
>> + */
>> +int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct 
>> drm_dp_aux *aux)
>> +{
>> +    struct dp_aux_backlight *bl;
>> +    struct backlight_properties props = { 0 };
>> +    u16 current_level;
>> +    u8 current_mode;
>> +    u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
>> +    int ret;
>> +
>> +    if (!panel || !panel->dev || !aux)
>> +        return -EINVAL;
>> +
>> +    ret = drm_dp_dpcd_read(aux, DP_EDP_DPCD_REV, edp_dpcd,
>> +                   EDP_DISPLAY_CTL_CAP_SIZE);
> 
> This creates a cyclic dependency between drm_kms_helper-ko and drm.ko. 
> drm_panel.c is in the latter, while drm_dp_dpcd_read() in 
> drm_dp_helper.c is in the former. Please fix.

FYI, build DRM as modules and the error shows up during make module_install.

Best regards
Thomas
Doug Anderson July 12, 2021, 1:39 p.m. UTC | #3 
Hi,

On Mon, Jul 12, 2021 at 2:41 AM Thomas Zimmermann <tzimmermann@suse.de> wrote:
>
> > +     ret = drm_dp_dpcd_read(aux, DP_EDP_DPCD_REV, edp_dpcd,
> > +                            EDP_DISPLAY_CTL_CAP_SIZE);
>
> This creates a cyclic dependency between drm_kms_helper-ko and drm.ko.
> drm_panel.c is in the latter, while drm_dp_dpcd_read() in
> drm_dp_helper.c is in the former. Please fix.

Yeah, this was reported Friday and I posted a patch to try to fix it:

https://lore.kernel.org/lkml/20210709152909.1.I23eb4cc5a680341e7b3e791632a635566fa5806a@changeid/

I see Rajeev had some feedback on it. Once I've dug out of my weekend
email hole I'll take a look at plan to post a v2 ASAP.

-Doug
Doug Anderson July 12, 2021, 3:03 p.m. UTC | #4 
Hi,

On Mon, Jul 12, 2021 at 6:39 AM Doug Anderson <dianders@chromium.org> wrote:
>
> Hi,
>
> On Mon, Jul 12, 2021 at 2:41 AM Thomas Zimmermann <tzimmermann@suse.de> wrote:
> >
> > > +     ret = drm_dp_dpcd_read(aux, DP_EDP_DPCD_REV, edp_dpcd,
> > > +                            EDP_DISPLAY_CTL_CAP_SIZE);
> >
> > This creates a cyclic dependency between drm_kms_helper-ko and drm.ko.
> > drm_panel.c is in the latter, while drm_dp_dpcd_read() in
> > drm_dp_helper.c is in the former. Please fix.
>
> Yeah, this was reported Friday and I posted a patch to try to fix it:
>
> https://lore.kernel.org/lkml/20210709152909.1.I23eb4cc5a680341e7b3e791632a635566fa5806a@changeid/
>
> I see Rajeev had some feedback on it. Once I've dug out of my weekend
> email hole I'll take a look at plan to post a v2 ASAP.

Breadcrumbs: v2 of the fix is at:

https://lore.kernel.org/lkml/20210712075933.v2.1.I23eb4cc5a680341e7b3e791632a635566fa5806a@changeid/

I'm hoping this looks OK so we can get this resolved before it trips
too many people up.

-Doug
diff mbox series

Patch

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index f634371..4fa1e3b 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -26,12 +26,20 @@ 
 #include <linux/module.h>
 
 #include <drm/drm_crtc.h>
+#include <drm/drm_dp_helper.h>
 #include <drm/drm_panel.h>
 #include <drm/drm_print.h>
 
 static DEFINE_MUTEX(panel_lock);
 static LIST_HEAD(panel_list);
 
+struct dp_aux_backlight {
+	struct backlight_device *base;
+	struct drm_dp_aux *aux;
+	struct drm_edp_backlight_info info;
+	bool enabled;
+};
+
 /**
  * DOC: drm panel
  *
@@ -342,6 +350,106 @@  int drm_panel_of_backlight(struct drm_panel *panel)
 	return 0;
 }
 EXPORT_SYMBOL(drm_panel_of_backlight);
+
+static int dp_aux_backlight_update_status(struct backlight_device *bd)
+{
+	struct dp_aux_backlight *bl = bl_get_data(bd);
+	u16 brightness = backlight_get_brightness(bd);
+	int ret = 0;
+
+	if (!backlight_is_blank(bd)) {
+		if (!bl->enabled) {
+			drm_edp_backlight_enable(bl->aux, &bl->info, brightness);
+			bl->enabled = true;
+			return 0;
+		}
+		ret = drm_edp_backlight_set_level(bl->aux, &bl->info, brightness);
+	} else {
+		if (bl->enabled) {
+			drm_edp_backlight_disable(bl->aux, &bl->info);
+			bl->enabled = false;
+		}
+	}
+
+	return ret;
+}
+
+static const struct backlight_ops dp_aux_bl_ops = {
+	.update_status = dp_aux_backlight_update_status,
+};
+
+/**
+ * drm_panel_dp_aux_backlight - create and use DP AUX backlight
+ * @panel: DRM panel
+ * @aux: The DP AUX channel to use
+ *
+ * Use this function to create and handle backlight if your panel
+ * supports backlight control over DP AUX channel using DPCD
+ * registers as per VESA's standard backlight control interface.
+ *
+ * When the panel is enabled backlight will be enabled after a
+ * successful call to &drm_panel_funcs.enable()
+ *
+ * When the panel is disabled backlight will be disabled before the
+ * call to &drm_panel_funcs.disable().
+ *
+ * A typical implementation for a panel driver supporting backlight
+ * control over DP AUX will call this function at probe time.
+ * Backlight will then be handled transparently without requiring
+ * any intervention from the driver.
+ *
+ * drm_panel_dp_aux_backlight() must be called after the call to drm_panel_init().
+ *
+ * Return: 0 on success or a negative error code on failure.
+ */
+int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux)
+{
+	struct dp_aux_backlight *bl;
+	struct backlight_properties props = { 0 };
+	u16 current_level;
+	u8 current_mode;
+	u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
+	int ret;
+
+	if (!panel || !panel->dev || !aux)
+		return -EINVAL;
+
+	ret = drm_dp_dpcd_read(aux, DP_EDP_DPCD_REV, edp_dpcd,
+			       EDP_DISPLAY_CTL_CAP_SIZE);
+	if (ret < 0)
+		return ret;
+
+	if (!drm_edp_backlight_supported(edp_dpcd)) {
+		DRM_DEV_INFO(panel->dev, "DP AUX backlight is not supported\n");
+		return 0;
+	}
+
+	bl = devm_kzalloc(panel->dev, sizeof(*bl), GFP_KERNEL);
+	if (!bl)
+		return -ENOMEM;
+
+	bl->aux = aux;
+
+	ret = drm_edp_backlight_init(aux, &bl->info, 0, edp_dpcd,
+				     &current_level, &current_mode);
+	if (ret < 0)
+		return ret;
+
+	props.type = BACKLIGHT_RAW;
+	props.brightness = current_level;
+	props.max_brightness = bl->info.max;
+
+	bl->base = devm_backlight_device_register(panel->dev, "dp_aux_backlight",
+						  panel->dev, bl,
+						  &dp_aux_bl_ops, &props);
+	if (IS_ERR(bl->base))
+		return PTR_ERR(bl->base);
+
+	panel->backlight = bl->base;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_panel_dp_aux_backlight);
 #endif
 
 MODULE_AUTHOR("Thierry Reding <treding@nvidia.com>");
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index 33605c3..3ebfaa6 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -32,6 +32,7 @@  struct backlight_device;
 struct device_node;
 struct drm_connector;
 struct drm_device;
+struct drm_dp_aux;
 struct drm_panel;
 struct display_timing;
 
@@ -64,8 +65,8 @@  enum drm_panel_orientation;
  * the panel. This is the job of the .unprepare() function.
  *
  * Backlight can be handled automatically if configured using
- * drm_panel_of_backlight(). Then the driver does not need to implement the
- * functionality to enable/disable backlight.
+ * drm_panel_of_backlight() or drm_panel_dp_aux_backlight(). Then the driver
+ * does not need to implement the functionality to enable/disable backlight.
  */
 struct drm_panel_funcs {
 	/**
@@ -144,8 +145,8 @@  struct drm_panel {
 	 * Backlight device, used to turn on backlight after the call
 	 * to enable(), and to turn off backlight before the call to
 	 * disable().
-	 * backlight is set by drm_panel_of_backlight() and drivers
-	 * shall not assign it.
+	 * backlight is set by drm_panel_of_backlight() or
+	 * drm_panel_dp_aux_backlight() and drivers shall not assign it.
 	 */
 	struct backlight_device *backlight;
 
@@ -208,11 +209,17 @@  static inline int of_drm_get_panel_orientation(const struct device_node *np,
 #if IS_ENABLED(CONFIG_DRM_PANEL) && (IS_BUILTIN(CONFIG_BACKLIGHT_CLASS_DEVICE) || \
 	(IS_MODULE(CONFIG_DRM) && IS_MODULE(CONFIG_BACKLIGHT_CLASS_DEVICE)))
 int drm_panel_of_backlight(struct drm_panel *panel);
+int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux);
 #else
 static inline int drm_panel_of_backlight(struct drm_panel *panel)
 {
 	return 0;
 }
+static inline int drm_panel_dp_aux_backlight(struct drm_panel *panel,
+					     struct drm_dp_aux *aux)
+{
+	return 0;
+}
 #endif
 
 #endif