Subject: Re: [PATCH v1 14/16] drm/panel: call prepare/enable only once

From: Laurent Pinchart <[email-masked]>
Date: Mon, 5 Aug 2019 13:59:28 +0300

Hi Sam,

Thank you for the patch.

On Sun, Aug 04, 2019 at 10:16:35PM +0200, Sam Ravnborg wrote:
> Many panel drivers duplicate logic to prevent prepare to be called
> for a panel that is already prepared.
> Likewise for enable.
> 
> Implement this logic in drm_panel so the individual drivers
> no longer needs this.
> A panel is considered prepared/enabled only if the prepare/enable call
> succeeds.
> For disable/unprepare it is unconditionally considered
> disabled/unprepared.
> 
> This allows calls to prepare/enable again, even if there were
> some issue disabling a regulator or similar during disable/unprepare.

Is this the right place to handle this ? Shouldn't the upper layers
ensure than enable/disable and prepare/unprepare are correcty balanced,
and not called multiple times ? Adding enabled and prepared state to
drm_panel not only doesn't align well with atomic state handling, but
also would hide issues in upper layers that should really be fixed
there.

> 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 | 66 ++++++++++++++++++++++++++++++-------
>  include/drm/drm_panel.h     | 21 ++++++++++++
>  2 files changed, 75 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index da19d5b4a2f4..0853764040de 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -66,10 +66,21 @@ EXPORT_SYMBOL(drm_panel_init);
>   */
>  int drm_panel_prepare(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->prepare)
> -		return panel->funcs->prepare(panel);
> +	int ret = -ENOSYS;
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (panel->prepared)
> +		return 0;
> +
> +	if (panel->funcs && panel->funcs->prepare)
> +		ret = panel->funcs->prepare(panel);
> +
> +	if (ret >= 0)
> +		panel->prepared = true;
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_panel_prepare);
>  
> @@ -85,10 +96,21 @@ EXPORT_SYMBOL(drm_panel_prepare);
>   */
>  int drm_panel_enable(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->enable)
> -		return panel->funcs->enable(panel);
> +	int ret = -ENOSYS;
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (panel->enabled)
> +		return 0;
> +
> +	if (panel->funcs && panel->funcs->enable)
> +		ret = panel->funcs->enable(panel);
> +
> +	if (ret >= 0)
> +		panel->enabled = true;
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_panel_enable);
>  
> @@ -104,10 +126,20 @@ EXPORT_SYMBOL(drm_panel_enable);
>   */
>  int drm_panel_disable(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->disable)
> -		return panel->funcs->disable(panel);
> +	int ret = -ENOSYS;
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (!panel->enabled)
> +		return 0;
> +
> +	if (panel->funcs && panel->funcs->disable)
> +		ret = panel->funcs->disable(panel);
> +
> +	panel->enabled = false;
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_panel_disable);
>  
> @@ -124,10 +156,20 @@ EXPORT_SYMBOL(drm_panel_disable);
>   */
>  int drm_panel_unprepare(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->unprepare)
> -		return panel->funcs->unprepare(panel);
> +	int ret = -ENOSYS;
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (!panel->prepared)
> +		return 0;
> +
> +	if (panel->funcs && panel->funcs->unprepare)
> +		ret = panel->funcs->unprepare(panel);
> +
> +	panel->prepared = false;
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_panel_unprepare);
>  
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 624bd15ecfab..7493500fc9bd 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -65,6 +65,9 @@ struct drm_panel_funcs {
>  	 * @prepare:
>  	 *
>  	 * Turn on panel and perform set up.
> +	 * When the panel is successfully prepared the prepare() function
> +	 * will not be called again until the panel has been unprepared.
> +	 *
>  	 */
>  	int (*prepare)(struct drm_panel *panel);
>  
> @@ -72,6 +75,8 @@ struct drm_panel_funcs {
>  	 * @enable:
>  	 *
>  	 * Enable panel (turn on back light, etc.).
> +	 * When the panel is successfully enabled the enable() function
> +	 * will not be called again until the panel has been disabled.
>  	 */
>  	int (*enable)(struct drm_panel *panel);
>  
> @@ -79,6 +84,7 @@ struct drm_panel_funcs {
>  	 * @disable:
>  	 *
>  	 * Disable panel (turn off back light, etc.).
> +	 * If the panel is already disabled the disable() function is not called.
>  	 */
>  	int (*disable)(struct drm_panel *panel);
>  
> @@ -86,6 +92,7 @@ struct drm_panel_funcs {
>  	 * @unprepare:
>  	 *
>  	 * Turn off panel.
> +	 * If the panel is already unprepared the unprepare() function is not called.
>  	 */
>  	int (*unprepare)(struct drm_panel *panel);
>  
> @@ -145,6 +152,20 @@ struct drm_panel {
>  	 * Panel entry in registry.
>  	 */
>  	struct list_head list;
> +
> +	/**
> +	 * @prepared:
> +	 *
> +	 * Set to true when the panel is successfully prepared.
> +	 */
> +	bool prepared;
> +
> +	/**
> +	 * @enabled:
> +	 *
> +	 * Set to true when the panel is successfully enabled.
> +	 */
> +	bool enabled;
>  };
>  
>  void drm_panel_init(struct drm_panel *panel);

-- 
Regards,

Laurent Pinchart

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