drm/bridge: Improve kerneldoc

Especially document the assumptions and semantics of the callbacks
carefully. Just a warm-up excercise really.

v2: Spelling fixes (Eric).

v3: Consolidate more with existing docs:

- Remove the overview section explaining the bridge funcs, that's
  now all in the drm_bridge_funcs kerneldoc in much more detail.

- Use & to reference structs so that kerneldoc automatically inserts
  hyperlinks.

v4: Review from Thierry.

Cc: Eric Anholt <eric@anholt.net>
Cc: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Archit Taneja <architt@codeaurora.org> (v3)
Link: http://patchwork.freedesktop.org/patch/msgid/1449218769-16577-7-git-send-email-daniel.vetter@ffwll.ch
Reviewed-by: Thierry Reding <treding@nvidia.com>

include/drm/drm_crtc.h

@@ -883,24 +883,114 @@ struct drm_plane {
 /**
  * struct drm_bridge_funcs - drm_bridge control functions
  * @attach: Called during drm_bridge_attach
- * @mode_fixup: Try to fixup (or reject entirely) proposed mode for this bridge
- * @disable: Called right before encoder prepare, disables the bridge
- * @post_disable: Called right after encoder prepare, for lockstepped disable
- * @mode_set: Set this mode to the bridge
- * @pre_enable: Called right before encoder commit, for lockstepped commit
- * @enable: Called right after encoder commit, enables the bridge
  */
 struct drm_bridge_funcs {
 	int (*attach)(struct drm_bridge *bridge);
+
+	/**
+	 * @mode_fixup:
+	 *
+	 * This callback is used to validate and adjust a mode. The paramater
+	 * mode is the display mode that should be fed to the next element in
+	 * the display chain, either the final &drm_connector or the next
+	 * &drm_bridge. The parameter adjusted_mode is the input mode the bridge
+	 * requires. It can be modified by this callback and does not need to
+	 * match mode.
+	 *
+	 * This is the only hook that allows a bridge to reject a modeset. If
+	 * this function passes all other callbacks must succeed for this
+	 * configuration.
+	 *
+	 * NOTE:
+	 *
+	 * This function is called in the check phase of atomic modesets, which
+	 * can be aborted for any reason (including on userspace's request to
+	 * just check whether a configuration would be possible). Drivers MUST
+	 * NOT touch any persistent state (hardware or software) or data
+	 * structures except the passed in adjusted_mode parameter.
+	 *
+	 * RETURNS:
+	 *
+	 * True if an acceptable configuration is possible, false if the modeset
+	 * operation should be rejected.
+	 */
 	bool (*mode_fixup)(struct drm_bridge *bridge,
 			   const struct drm_display_mode *mode,
 			   struct drm_display_mode *adjusted_mode);
+	/**
+	 * @disable:
+	 *
+	 * This callback should disable the bridge. It is called right before
+	 * the preceding element in the display pipe is disabled. If the
+	 * preceding element is a bridge this means it's called before that
+	 * bridge's ->disable() function. If the preceding element is a
+	 * &drm_encoder it's called right before the encoder's ->disable(),
+	 * ->prepare() or ->dpms() hook from struct &drm_encoder_helper_funcs.
+	 *
+	 * The bridge can assume that the display pipe (i.e. clocks and timing
+	 * signals) feeding it is still running when this callback is called.
+	 */
 	void (*disable)(struct drm_bridge *bridge);
+
+	/**
+	 * @post_disable:
+	 *
+	 * This callback should disable the bridge. It is called right after
+	 * the preceding element in the display pipe is disabled. If the
+	 * preceding element is a bridge this means it's called after that
+	 * bridge's ->post_disable() function. If the preceding element is a
+	 * &drm_encoder it's called right after the encoder's ->disable(),
+	 * ->prepare() or ->dpms() hook from struct &drm_encoder_helper_funcs.
+	 *
+	 * The bridge must assume that the display pipe (i.e. clocks and timing
+	 * singals) feeding it is no longer running when this callback is
+	 * called.
+	 */
 	void (*post_disable)(struct drm_bridge *bridge);
+
+	/**
+	 * @mode_set:
+	 *
+	 * This callback should set the given mode on the bridge. It is called
+	 * after the ->mode_set() callback for the preceding element in the
+	 * display pipeline has been called already. The display pipe (i.e.
+	 * clocks and timing signals) is off when this function is called.
+	 */
 	void (*mode_set)(struct drm_bridge *bridge,
 			 struct drm_display_mode *mode,
 			 struct drm_display_mode *adjusted_mode);
+	/**
+	 * @pre_enable:
+	 *
+	 * This callback should enable the bridge. It is called right before
+	 * the preceding element in the display pipe is enabled. If the
+	 * preceding element is a bridge this means it's called before that
+	 * bridge's ->pre_enable() function. If the preceding element is a
+	 * &drm_encoder it's called right before the encoder's ->enable(),
+	 * ->commit() or ->dpms() hook from struct &drm_encoder_helper_funcs.
+	 *
+	 * The display pipe (i.e. clocks and timing signals) feeding this bridge
+	 * will not yet be running when this callback is called. The bridge must
+	 * not enable the display link feeding the next bridge in the chain (if
+	 * there is one) when this callback is called.
+	 */
 	void (*pre_enable)(struct drm_bridge *bridge);
+
+	/**
+	 * @enable:
+	 *
+	 * This callback should enable the bridge. It is called right after
+	 * the preceding element in the display pipe is enabled. If the
+	 * preceding element is a bridge this means it's called after that
+	 * bridge's ->enable() function. If the preceding element is a
+	 * &drm_encoder it's called right after the encoder's ->enable(),
+	 * ->commit() or ->dpms() hook from struct &drm_encoder_helper_funcs.
+	 *
+	 * The bridge can assume that the display pipe (i.e. clocks and timing
+	 * signals) feeding it is running when this callback is called. This
+	 * callback must enable the display link feeding the next bridge in the
+	 * chain if there is one.
+	 */
 	void (*enable)(struct drm_bridge *bridge);
 };