Re: [RFC PATCH 1/3] drm/panel: Support panel detection

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Apr 30, 2018 at 04:43:21PM +0200, Boris Brezillon wrote:
> Some panels might be connected through extension boards and might not
> be available when the system boots. Extend the panel interface to
> support panel detection.
> 
> An optional ->detect() hook is added and, if implemented, will be called
> every time the panel user wants to know if the panel is connected or
> disconnected.
> 
> We also add a ->polled field which should encode the type of polling the
> DRM core should do (DRM_CONNECTOR_POLL_HPD, DRM_CONNECTOR_POLL_CONNECT
> and DRM_CONNECTOR_POLL_DISCONNECT flags).
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>

Hm, not sure panel detection makes much sense, the entire idea behind
drm_panel is to hard-code a fixed/built-in panel. The only thing panels
may report through the connection status is whether the lid is closed or
not. Yes we should probably document that somewhere.

If you have a panel-that-can-be-hotplugged a drm_bridge that implemens the
drm_connector is probably the way to go.

> ---
>  include/drm/drm_panel.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 14ac240a1f64..718cc1f746ab 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 <drm/drm_connector.h>
>  #include <linux/errno.h>
>  #include <linux/list.h>
>  
> @@ -68,6 +69,7 @@ struct display_timing;
>   * the panel. This is the job of the .unprepare() function.
>   */
>  struct drm_panel_funcs {
> +	int (*detect)(struct drm_panel *panel);

Kerneldoc for this please. Would also be really good to switch this struct
of function pointers over to the in-line style, and put the paragraphs
relevant for a given callback into it's dedicated comment.
-Daniel

>  	int (*disable)(struct drm_panel *panel);
>  	int (*unprepare)(struct drm_panel *panel);
>  	int (*prepare)(struct drm_panel *panel);
> @@ -90,6 +92,7 @@ struct drm_panel {
>  	struct drm_connector *connector;
>  	struct device *dev;
>  
> +	u8 polled;
>  	const struct drm_panel_funcs *funcs;
>  
>  	struct list_head list;
> @@ -186,6 +189,15 @@ static inline int drm_panel_get_modes(struct drm_panel *panel)
>  	return panel ? -ENOSYS : -EINVAL;
>  }
>  
> +static inline int drm_panel_detect(struct drm_panel *panel)
> +{
> +	if (panel && panel->funcs && panel->funcs->detect)
> +		return panel->funcs->detect(panel);
> +
> +	/* Consider the panel as connected by default. */
> +	return panel ? connector_status_connected : -EINVAL;
> +}
> +
>  void drm_panel_init(struct drm_panel *panel);
>  
>  int drm_panel_add(struct drm_panel *panel);
> -- 
> 2.14.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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