Re: [PATCH v2 01/25] drm/drm_panel: no error when no callback

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sam,

Thank you for the patch.

On Sat, Dec 07, 2019 at 03:03:29PM +0100, Sam Ravnborg wrote:
> The callbacks in drm_panel_funcs are optional, so do not
> return an error just because no callback is assigned.
> 
> v2:
> - Document what functions in drm_panel_funcs are optional (Laurent)
> - Return -EOPNOTSUPP if get_modes() is not assigned (Laurent)
>   (Sam: -EOPNOTSUPP seems to best error code in this situation)
> 
> Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Thierry Reding <thierry.reding@gmail.com>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> ---
>  drivers/gpu/drm/drm_panel.c | 35 +++++++++++++++++++++++++----------
>  include/drm/drm_panel.h     | 18 ++++++++++++++++--
>  2 files changed, 41 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index ed7985c0535a..4ab7229fb22b 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -151,10 +151,13 @@ EXPORT_SYMBOL(drm_panel_detach);
>   */
>  int drm_panel_prepare(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->prepare)
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (panel->funcs && panel->funcs->prepare)
>  		return panel->funcs->prepare(panel);
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	return 0;
>  }
>  EXPORT_SYMBOL(drm_panel_prepare);
>  
> @@ -171,10 +174,13 @@ EXPORT_SYMBOL(drm_panel_prepare);
>   */
>  int drm_panel_unprepare(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->unprepare)
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (panel->funcs && panel->funcs->unprepare)
>  		return panel->funcs->unprepare(panel);
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	return 0;
>  }
>  EXPORT_SYMBOL(drm_panel_unprepare);
>  
> @@ -190,10 +196,13 @@ EXPORT_SYMBOL(drm_panel_unprepare);
>   */
>  int drm_panel_enable(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->enable)
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (panel->funcs && panel->funcs->enable)
>  		return panel->funcs->enable(panel);
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	return 0;
>  }
>  EXPORT_SYMBOL(drm_panel_enable);
>  
> @@ -209,10 +218,13 @@ EXPORT_SYMBOL(drm_panel_enable);
>   */
>  int drm_panel_disable(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->disable)
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (panel->funcs && panel->funcs->disable)
>  		return panel->funcs->disable(panel);
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	return 0;
>  }
>  EXPORT_SYMBOL(drm_panel_disable);
>  
> @@ -228,10 +240,13 @@ EXPORT_SYMBOL(drm_panel_disable);
>   */
>  int drm_panel_get_modes(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->get_modes)
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (panel->funcs && panel->funcs->get_modes)
>  		return panel->funcs->get_modes(panel);
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	return -EOPNOTSUPP;
>  }
>  EXPORT_SYMBOL(drm_panel_get_modes);
>  
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index ce8da64022b4..d71655b2634c 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -65,6 +65,8 @@ struct drm_panel_funcs {
>  	 * @prepare:
>  	 *
>  	 * Turn on panel and perform set up.
> +	 *
> +	 * This function is optional.
>  	 */
>  	int (*prepare)(struct drm_panel *panel);
>  
> @@ -72,6 +74,8 @@ struct drm_panel_funcs {
>  	 * @enable:
>  	 *
>  	 * Enable panel (turn on back light, etc.).
> +	 *
> +	 * This function is optional.
>  	 */
>  	int (*enable)(struct drm_panel *panel);
>  
> @@ -79,6 +83,8 @@ struct drm_panel_funcs {
>  	 * @disable:
>  	 *
>  	 * Disable panel (turn off back light, etc.).
> +	 *
> +	 * This function is optional.
>  	 */
>  	int (*disable)(struct drm_panel *panel);
>  
> @@ -86,14 +92,20 @@ struct drm_panel_funcs {
>  	 * @unprepare:
>  	 *
>  	 * Turn off panel.
> +	 *
> +	 * This function is optional.
>  	 */
>  	int (*unprepare)(struct drm_panel *panel);
>  
>  	/**
>  	 * @get_modes:
>  	 *
> -	 * Add modes to the connector that the panel is attached to and
> -	 * return the number of modes added.
> +	 * Add modes to the connector that the panel is attached to.
> +	 *
> +	 * This function is mandatory.
> +	 *
> +	 * Returns the number of modes added, -EOPNOTSUPP if callback
> +	 * is missing, -EINVAL if panel is NULL.

This applies to drm_panel_get_modes, not &drm_panel_funcs.get_modes.
Here you should just have

 	 *
 	 * Add modes to the connector that the panel is attached to and
 	 * return the number of modes added.
+	 *
+	 * This function is mandatory.
 	 */
 	int (*get_modes)(struct drm_panel *panel);
 
>  	 */
>  	int (*get_modes)(struct drm_panel *panel);
>  
> @@ -102,6 +114,8 @@ struct drm_panel_funcs {
>  	 *
>  	 * Copy display timings into the provided array and return
>  	 * the number of display timings available.
> +	 *
> +	 * This function is optional.
>  	 */
>  	int (*get_timings)(struct drm_panel *panel, unsigned int num_timings,
>  			   struct display_timing *timings);

-- 
Regards,

Laurent Pinchart

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