Subject: Re: [PATCH v1 01/26] drm/drm_panel: no error when no callback

From: Laurent Pinchart <[email-masked]>
Date: Tue, 3 Dec 2019 08:24:59 +0200

Hi Sam,

Thank you for the patch.

On Mon, Dec 02, 2019 at 08:32:05PM +0100, Sam Ravnborg wrote:
> The callbacks in drm_panel_funcs are optional, so do not
> return an error just because no callback is assigned.

Unless I'm mistaken the callbacks are not documented as optional. Should
this be fixed too ?

> Signed-off-by: Sam Ravnborg <[email-masked]>
> Cc: Maarten Lankhorst <[email-masked]>
> Cc: Maxime Ripard <[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 | 35 +++++++++++++++++++++++++----------
>  1 file changed, 25 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index ed7985c0535a..2d59cdd05e50 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);

Should get_modes() be optional ? As far as I can tell all the panel
drivers in drivers/gpu/drm/panel/ implement it, and I'm not sure to see
how a panel could be usable if it can't return its mode.

On the other hand you return 0 if the callback isn't implemented, which
doesn't mean success here, so I suppose that's fine, but I don't think
we should document .get_modes() as being optional.

With these issues addressed (if they need to be),

Reviewed-by: Laurent Pinchart <[email-masked]>

>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	return 0;
>  }
>  EXPORT_SYMBOL(drm_panel_get_modes);
>  

-- 
Regards,

Laurent Pinchart

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