Subject: Re: [PATCH v1 15/16] drm/panel: add backlight support

From: Laurent Pinchart <[email-masked]>
Date: Mon, 5 Aug 2019 14:04:32 +0300

Hi Sam,

Thank you for the patch.

On Sun, Aug 04, 2019 at 10:16:36PM +0200, Sam Ravnborg wrote:
> Panels often supports backlight as specified in a device tree.
> Update the drm_panel infrastructure to support this to
> simplify the drivers.
> 
> With this the panel driver just needs to add the following to the
> probe() function:
> 
>     err = drm_panel_of_backlight(panel);
>     if (err)
>             return err;
> 
> Then drm_panel will handle all the rest.

Do you have an example on how this will simplify drivers ? How many
existing panel drivers would benefit from this, and do you plan to
convert them ?

> 
> Signed-off-by: Sam Ravnborg <[email-masked]>
> Cc: Maarten Lankhorst <[email-masked]>
> Cc: Maxime Ripard <[email-masked]>
> Cc: Sean Paul <[email-masked]>
> Cc: Thierry Reding <[email-masked]>
> Cc: Sam Ravnborg <[email-masked]>
> Cc: David Airlie <[email-masked]>
> Cc: Daniel Vetter <[email-masked]>
> ---
>  drivers/gpu/drm/drm_panel.c | 41 +++++++++++++++++++++++++++++++++++++
>  include/drm/drm_panel.h     | 23 +++++++++++++++++++++
>  2 files changed, 64 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index 0853764040de..d8139674b883 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -21,6 +21,7 @@
>   * DEALINGS IN THE SOFTWARE.
>   */
>  
> +#include <linux/backlight.h>
>  #include <linux/err.h>
>  #include <linux/module.h>
>  
> @@ -110,6 +111,7 @@ int drm_panel_enable(struct drm_panel *panel)
>  	if (ret >= 0)
>  		panel->enabled = true;
>  
> +	backlight_enable(panel->backlight);
>  	return ret;
>  }
>  EXPORT_SYMBOL(drm_panel_enable);
> @@ -134,6 +136,8 @@ int drm_panel_disable(struct drm_panel *panel)
>  	if (!panel->enabled)
>  		return 0;
>  
> +	backlight_disable(panel->backlight);
> +
>  	if (panel->funcs && panel->funcs->disable)
>  		ret = panel->funcs->disable(panel);
>  
> @@ -308,6 +312,43 @@ struct drm_panel *of_drm_find_panel(const struct device_node *np)
>  EXPORT_SYMBOL(of_drm_find_panel);
>  #endif
>  
> +#ifdef CONFIG_BACKLIGHT_CLASS_DEVICE
> +/**
> + * drm_panel_of_backlight - use backlight device node for backlight
> + * @panel: DRM panel
> + *
> + * Use this function to enable backlight handling if your panel
> + * uses device tree and has a backlight handle.
> + *
> + * When panel is enabled backlight will be enabled after a
> + * successfull call to &drm_panel_funcs.enable()
> + *
> + * When panel is disabled backlight will be disabled before the
> + * call to &drm_panel_funcs.disable().
> + *
> + * A typical implementation for a panel driver supporting device tree
> + * will call this function and then backlight just works.
> + *
> + * Return: 0 on success or a negative error code on failure.
> + */
> +int drm_panel_of_backlight(struct drm_panel *panel)
> +{
> +	struct backlight_device *backlight;
> +
> +	if (!panel || !panel->dev)
> +		return -EINVAL;
> +
> +	backlight = devm_of_find_backlight(panel->dev);
> +
> +	if (IS_ERR(backlight))
> +                return PTR_ERR(backlight);
> +
> +	panel->backlight = backlight;
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_panel_of_backlight);
> +#endif
> +
>  MODULE_AUTHOR("Thierry Reding <[email-masked]>");
>  MODULE_DESCRIPTION("DRM panel infrastructure");
>  MODULE_LICENSE("GPL and additional rights");
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 7493500fc9bd..31349c2393b7 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -28,6 +28,7 @@
>  #include <linux/errno.h>
>  #include <linux/list.h>
>  
> +struct backlight_device;
>  struct device_node;
>  struct drm_connector;
>  struct drm_device;
> @@ -59,6 +60,10 @@ struct display_timing;
>   *
>   * To save power when no video data is transmitted, a driver can power down
>   * 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 do not need to implement the
> + * functionality to enable/disable backlight.
>   */
>  struct drm_panel_funcs {
>  	/**
> @@ -139,6 +144,15 @@ struct drm_panel {
>  	 */
>  	struct device *dev;
>  
> +	/**
> +	 * @backlight:
> +	 *
> +	 * Backlight device, used to turn on backlight after
> +	 * the call to enable(), and to turn off
> +	 * backlight before call to disable().
> +	 */
> +	struct backlight_device *backlight;
> +
>  	/**
>  	 * @funcs:
>  	 *
> @@ -193,4 +207,13 @@ static inline struct drm_panel *of_drm_find_panel(const struct device_node *np)
>  }
>  #endif
>  
> +#if defined(CONFIG_BACKLIGHT_CLASS_DEVICE) && defined(CONFIG_DRM_PANEL)
> +int drm_panel_of_backlight(struct drm_panel *panel);

I would expect callers of this function to depend on (or select)
CONFIG_DRM_PANEL, so I would drop it from here.

> +#else
> +static inline int drm_panel_of_backlight(struct drm_panel *panel)
> +{
> +	return -EINVAL;

Maybe -ENOSYS ?

> +}
> +#endif
> +
>  #endif

-- 
Regards,

Laurent Pinchart

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