drm: Document drm_connector_funcs

The special case here is that both ->detect and ->force are actually
functions only called by the probe helpers and hence really shouldn't
be here. But since they've used by pretty much every driver I figured
it's better to just document this for now instead of holding this doc
patch hostage until that's all fixed. For that reason also group force
right next to detect.

v2: Use FIXME comments to annotate where we should move a hook to
helpers.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449218769-16577-18-git-send-email-daniel.vetter@ffwll.ch
Reviewed-by: Thierry Reding <treding@nvidia.com>

include/drm/drm_crtc.h

@@ -617,16 +617,28 @@ struct drm_connector_state {
 
 /**
  * struct drm_connector_funcs - control connectors on a given device
- * @dpms: set power state
- * @detect: is this connector active?
- * @fill_modes: fill mode list for this connector
- * @force: notify the driver that the connector is forced on
  *
  * Each CRTC may have one or more connectors attached to it.  The functions
  * below allow the core DRM code to control connectors, enumerate available modes,
  * etc.
  */
 struct drm_connector_funcs {
+	/**
+	 * @dpms:
+	 *
+	 * Legacy entry point to set the per-connector DPMS state. Legacy DPMS
+	 * is exposed as a standard property on the connector, but diverted to
+	 * this callback in the drm core. Note that atomic drivers don't
+	 * implement the 4 level DPMS support on the connector any more, but
+	 * instead only have an on/off "ACTIVE" property on the CRTC object.
+	 *
+	 * Drivers implementing atomic modeset should use
+	 * drm_atomic_helper_connector_dpms() to implement this hook.
+	 *
+	 * RETURNS:
+	 *
+	 * 0 on success or a negative error code on failure.
+	 */
 	int (*dpms)(struct drm_connector *connector, int mode);
 
 	/**
@@ -641,14 +653,67 @@ struct drm_connector_funcs {
 	 */
 	void (*reset)(struct drm_connector *connector);
 
-	/* Check to see if anything is attached to the connector.
-	 * @force is set to false whilst polling, true when checking the
-	 * connector due to user request. @force can be used by the driver
-	 * to avoid expensive, destructive operations during automated
-	 * probing.
+	/**
+	 * @detect:
+	 *
+	 * Check to see if anything is attached to the connector. The parameter
+	 * force is set to false whilst polling, true when checking the
+	 * connector due to a user request. force can be used by the driver to
+	 * avoid expensive, destructive operations during automated probing.
+	 *
+	 * FIXME:
+	 *
+	 * Note that this hook is only called by the probe helper. It's not in
+	 * the helper library vtable purely for historical reasons. The only DRM
+	 * core	entry point to probe connector state is @fill_modes.
+	 *
+	 * RETURNS:
+	 *
+	 * drm_connector_status indicating the connector's status.
 	 */
 	enum drm_connector_status (*detect)(struct drm_connector *connector,
 					    bool force);
+
+	/**
+	 * @force:
+	 *
+	 * This function is called to update internal encoder state when the
+	 * connector is forced to a certain state by userspace, either through
+	 * the sysfs interfaces or on the kernel cmdline. In that case the
+	 * @detect callback isn't called.
+	 *
+	 * FIXME:
+	 *
+	 * Note that this hook is only called by the probe helper. It's not in
+	 * the helper library vtable purely for historical reasons. The only DRM
+	 * core	entry point to probe connector state is @fill_modes.
+	 */
+	void (*force)(struct drm_connector *connector);
+
+	/**
+	 * @fill_modes:
+	 *
+	 * Entry point for output detection and basic mode validation. The
+	 * driver should reprobe the output if needed (e.g. when hotplug
+	 * handling is unreliable), add all detected modes to connector->modes
+	 * and filter out any the device can't support in any configuration. It
+	 * also needs to filter out any modes wider or higher than the
+	 * parameters max_width and max_height indicate.
+	 *
+	 * The drivers must also prune any modes no longer valid from
+	 * connector->modes. Furthermore it must update connector->status and
+	 * connector->edid.  If no EDID has been received for this output
+	 * connector->edid must be NULL.
+	 *
+	 * Drivers using the probe helpers should use
+	 * drm_helper_probe_single_connector_modes() or
+	 * drm_helper_probe_single_connector_modes_nomerge() to implement this
+	 * function.
+	 *
+	 * RETURNS:
+	 *
+	 * The number of modes detected and filled into connector->modes.
+	 */
 	int (*fill_modes)(struct drm_connector *connector, uint32_t max_width, uint32_t max_height);
 
 	/**
@@ -679,7 +744,6 @@ struct drm_connector_funcs {
 	 * connector hotplugging (e.g. DisplayPort MST).
 	 */
 	void (*destroy)(struct drm_connector *connector);
-	void (*force)(struct drm_connector *connector);
 
 	/**
 	 * @atomic_duplicate_state: