[PATCH v2 01/10] drm/panel: Keep track of enabled/prepared

[Andrzej Hajda]

On 12.10.2017 19:55, Sean Paul wrote:
> This patch adds state tracking to the drm_panel functions which keep
> track of enabled and prepared. If the calls are unbalanced, a WARNING is
> issued.
>
> The motivation for this change is that a number of panel drivers
> (including panel-simple) all do this to protect their regulator
> refcounts. The atomic framework ensures the calls are balanced, and
> there  aren't any panel drivers being used by legacy drivers. As such,
> these checks are useless, but let's add a WARNING just in case something
> crazy happens (like a legacy driver using a panel).
>
> Less code == better.
>
> Changes in v2:
>  - Reduced enabled/prepared bools to one enum (Andrzej)
>  - Don't update state if the operation fails (Andrzej)
>  - Issue warning even if operation is not implemented
>
> Cc: Andrzej Hajda <a.hajda at samsung.com>
> Signed-off-by: Sean Paul <seanpaul at chromium.org>
> ---
>  drivers/gpu/drm/drm_panel.c |  1 +
>  include/drm/drm_panel.h     | 60 +++++++++++++++++++++++++++++++++++++++------
>  2 files changed, 53 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index 308d442a531b..e5957e7da768 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -48,6 +48,7 @@ static LIST_HEAD(panel_list);
>  void drm_panel_init(struct drm_panel *panel)
>  {
>  	INIT_LIST_HEAD(&panel->list);
> +	panel->state = DRM_PANEL_POWER_OFF;
>  }
>  EXPORT_SYMBOL(drm_panel_init);
>  
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 14ac240a1f64..425461c4c574 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -24,6 +24,7 @@
>  #ifndef __DRM_PANEL_H__
>  #define __DRM_PANEL_H__
>  
> +#include <linux/bug.h>
>  #include <linux/errno.h>
>  #include <linux/list.h>
>  
> @@ -84,6 +85,7 @@ struct drm_panel_funcs {
>   * @dev: parent device of the panel
>   * @funcs: operations that can be performed on the panel
>   * @list: panel entry in registry
> + * @power_state: keeps track of the panel power status
>   */
>  struct drm_panel {
>  	struct drm_device *drm;
> @@ -93,6 +95,12 @@ struct drm_panel {
>  	const struct drm_panel_funcs *funcs;
>  
>  	struct list_head list;
> +
> +	enum {
> +		DRM_PANEL_POWER_OFF,
> +		DRM_PANEL_POWER_PREPARED,
> +		DRM_PANEL_POWER_ENABLED
> +	} state;
>  };
>  
>  /**
> @@ -104,12 +112,21 @@ struct drm_panel {
>   * is usually no longer possible to communicate with the panel until another
>   * call to drm_panel_prepare().
>   *
> + * Atomic framework should ensure that prepare/unprepare are properly balanced.
> + * If this is not the case, a WARNING will be issued.
> + *
>   * Return: 0 on success or a negative error code on failure.
>   */
>  static inline int drm_panel_unprepare(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->unprepare)
> -		return panel->funcs->unprepare(panel);
> +	WARN_ON(panel->state != DRM_PANEL_POWER_PREPARED);
> +
> +	if (panel && panel->funcs && panel->funcs->unprepare) {
> +		int ret = panel->funcs->unprepare(panel);
> +		if (!ret)
> +			panel->state = DRM_PANEL_POWER_OFF;
> +		return ret;
> +	}
>  
>  	return panel ? -ENOSYS : -EINVAL;

State check and state change should be performed also for panels without
callbacks, otherwise it will work only with panels having full set of
callbacks.
Another thing is that missing callback does not mean
function-not-implemented (ENOSYS), it is rather nothing-to-do, in such
case function should return rather 0, this will simplify also error
handling on callers side.

And one thing just to consider: all functions have almost the same body,
maybe it would be good to use some helper, for example:

    #define drm_panel_state_change(panel, from, to, func) ...

    int drm_panel_unprepare(struct drm_panel *panel)
    {
        return drm_panel_state_change(panel, DRM_PANEL_POWER_PREPARED,
DRM_PANEL_POWER_OFF, unprepare);
    }


Regards
Andrzej
>  }
> @@ -122,12 +139,21 @@ static inline int drm_panel_unprepare(struct drm_panel *panel)
>   * drivers. For smart panels it should still be possible to communicate with
>   * the integrated circuitry via any command bus after this call.
>   *
> + * Atomic framework should ensure that enable/disable are properly balanced.
> + * If this is not the case, a WARNING will be issued.
> + *
>   * Return: 0 on success or a negative error code on failure.
>   */
>  static inline int drm_panel_disable(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->disable)
> -		return panel->funcs->disable(panel);
> +	WARN_ON(panel->state != DRM_PANEL_POWER_ENABLED);
> +
> +	if (panel && panel->funcs && panel->funcs->disable) {
> +		int ret = panel->funcs->disable(panel);
> +		if (!ret)
> +			panel->state = DRM_PANEL_POWER_PREPARED;
> +		return ret;
> +	}
>  
>  	return panel ? -ENOSYS : -EINVAL;
>  }
> @@ -140,12 +166,21 @@ static inline int drm_panel_disable(struct drm_panel *panel)
>   * the panel. After this has completed it is possible to communicate with any
>   * integrated circuitry via a command bus.
>   *
> + * Atomic framework should ensure that prepare/unprepare are properly balanced.
> + * If this is not the case, a WARNING will be issued.
> + *
>   * Return: 0 on success or a negative error code on failure.
>   */
>  static inline int drm_panel_prepare(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->prepare)
> -		return panel->funcs->prepare(panel);
> +	WARN_ON(panel->state != DRM_PANEL_POWER_OFF);
> +
> +	if (panel && panel->funcs && panel->funcs->prepare) {
> +		int ret = panel->funcs->prepare(panel);
> +		if (!ret)
> +			panel->state = DRM_PANEL_POWER_PREPARED;
> +		return ret;
> +	}
>  
>  	return panel ? -ENOSYS : -EINVAL;
>  }
> @@ -158,12 +193,21 @@ static inline int drm_panel_prepare(struct drm_panel *panel)
>   * and the backlight to be enabled. Content will be visible on screen after
>   * this call completes.
>   *
> + * Atomic framework should ensure that enable/disable are properly balanced.
> + * If this is not the case, a WARNING will be issued.
> + *
>   * Return: 0 on success or a negative error code on failure.
>   */
>  static inline int drm_panel_enable(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->enable)
> -		return panel->funcs->enable(panel);
> +	WARN_ON(panel->state != DRM_PANEL_POWER_PREPARED);
> +
> +	if (panel && panel->funcs && panel->funcs->enable) {
> +		int ret = panel->funcs->enable(panel);
> +		if (!ret)
> +			panel->state = DRM_PANEL_POWER_ENABLED;
> +		return ret;
> +	}
>  
>  	return panel ? -ENOSYS : -EINVAL;
>  }