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>

drivers/gpu/drm/drm_bridge.c

@@ -31,14 +31,14 @@
 /**
  * DOC: overview
  *
- * drm_bridge represents a device that hangs on to an encoder. These are handy
- * when a regular drm_encoder entity isn't enough to represent the entire
+ * struct &drm_bridge represents a device that hangs on to an encoder. These are
+ * handy when a regular &drm_encoder entity isn't enough to represent the entire
  * encoder chain.
  *
- * A bridge is always associated to a single drm_encoder at a time, but can be
+ * A bridge is always attached to a single &drm_encoder at a time, but can be
  * either connected to it directly, or through an intermediate bridge:
  *
- * encoder ---> bridge B ---> bridge A
+ *     encoder ---> bridge B ---> bridge A
  *
  * Here, the output of the encoder feeds to bridge B, and that furthers feeds to
  * bridge A.
@@ -46,11 +46,16 @@
  * The driver using the bridge is responsible to make the associations between
  * the encoder and bridges. Once these links are made, the bridges will
  * participate along with encoder functions to perform mode_set/enable/disable
- * through the ops provided in drm_bridge_funcs.
+ * through the ops provided in &drm_bridge_funcs.
  *
  * drm_bridge, like drm_panel, aren't drm_mode_object entities like planes,
- * crtcs, encoders or connectors. They just provide additional hooks to get the
- * desired output at the end of the encoder chain.
+ * CRTCs, encoders or connectors and hence are not visible to userspace. They
+ * just provide additional hooks to get the desired output at the end of the
+ * encoder chain.
+ *
+ * Bridges can also be chained up using the next pointer in struct &drm_bridge.
+ *
+ * Both legacy CRTC helpers and the new atomic modeset helpers support bridges.
  */
 
 static DEFINE_MUTEX(bridge_lock);
@@ -122,34 +127,12 @@ EXPORT_SYMBOL(drm_bridge_attach);
 /**
  * DOC: bridge callbacks
  *
- * The drm_bridge_funcs ops are populated by the bridge driver. The drm
- * internals(atomic and crtc helpers) use the helpers defined in drm_bridge.c
- * These helpers call a specific drm_bridge_funcs op for all the bridges
+ * The &drm_bridge_funcs ops are populated by the bridge driver. The DRM
+ * internals (atomic and CRTC helpers) use the helpers defined in drm_bridge.c
+ * These helpers call a specific &drm_bridge_funcs op for all the bridges
  * during encoder configuration.
  *
- * When creating a bridge driver, one can implement drm_bridge_funcs op with
- * the help of these rough rules:
- *
- * pre_enable: this contains things needed to be done for the bridge before
- * its clock and timings are enabled by its source. For a bridge, its source
- * is generally the encoder or bridge just before it in the encoder chain.
- *
- * enable: this contains things needed to be done for the bridge once its
- * source is enabled. In other words, enable is called once the source is
- * ready with clock and timing needed by the bridge.
- *
- * disable: this contains things needed to be done for the bridge assuming
- * that its source is still enabled, i.e. clock and timings are still on.
- *
- * post_disable: this contains things needed to be done for the bridge once
- * its source is disabled, i.e. once clocks and timings are off.
- *
- * mode_fixup: this should fixup the given mode for the bridge. It is called
- * after the encoder's mode fixup. mode_fixup can also reject a mode completely
- * if it's unsuitable for the hardware.
- *
- * mode_set: this sets up the mode for the bridge. It assumes that its source
- * (an encoder or a bridge) has set the mode too.
+ * For detailed specification of the bridge callbacks see &drm_bridge_funcs.
  */
 
 /**
@@ -159,7 +142,7 @@ EXPORT_SYMBOL(drm_bridge_attach);
  * @mode: desired mode to be set for the bridge
  * @adjusted_mode: updated mode that works for this bridge
  *
- * Calls 'mode_fixup' drm_bridge_funcs op for all the bridges in the
+ * Calls ->mode_fixup() &drm_bridge_funcs op for all the bridges in the
  * encoder chain, starting from the first bridge to the last.
  *
  * Note: the bridge passed should be the one closest to the encoder
@@ -186,11 +169,11 @@ bool drm_bridge_mode_fixup(struct drm_bridge *bridge,
 EXPORT_SYMBOL(drm_bridge_mode_fixup);
 
 /**
- * drm_bridge_disable - calls 'disable' drm_bridge_funcs op for all
+ * drm_bridge_disable - calls ->disable() &drm_bridge_funcs op for all
  *			bridges in the encoder chain.
  * @bridge: bridge control structure
  *
- * Calls 'disable' drm_bridge_funcs op for all the bridges in the encoder
+ * Calls ->disable() &drm_bridge_funcs op for all the bridges in the encoder
  * chain, starting from the last bridge to the first. These are called before
  * calling the encoder's prepare op.
  *
@@ -208,11 +191,11 @@ void drm_bridge_disable(struct drm_bridge *bridge)
 EXPORT_SYMBOL(drm_bridge_disable);
 
 /**
- * drm_bridge_post_disable - calls 'post_disable' drm_bridge_funcs op for
+ * drm_bridge_post_disable - calls ->post_disable() &drm_bridge_funcs op for
  *			     all bridges in the encoder chain.
  * @bridge: bridge control structure
  *
- * Calls 'post_disable' drm_bridge_funcs op for all the bridges in the
+ * Calls ->post_disable() &drm_bridge_funcs op for all the bridges in the
  * encoder chain, starting from the first bridge to the last. These are called
  * after completing the encoder's prepare op.
  *
@@ -236,7 +219,7 @@ EXPORT_SYMBOL(drm_bridge_post_disable);
  * @mode: desired mode to be set for the bridge
  * @adjusted_mode: updated mode that works for this bridge
  *
- * Calls 'mode_set' drm_bridge_funcs op for all the bridges in the
+ * Calls ->mode_set() &drm_bridge_funcs op for all the bridges in the
  * encoder chain, starting from the first bridge to the last.
  *
  * Note: the bridge passed should be the one closest to the encoder
@@ -256,11 +239,11 @@ void drm_bridge_mode_set(struct drm_bridge *bridge,
 EXPORT_SYMBOL(drm_bridge_mode_set);
 
 /**
- * drm_bridge_pre_enable - calls 'pre_enable' drm_bridge_funcs op for all
+ * drm_bridge_pre_enable - calls ->pre_enable() &drm_bridge_funcs op for all
  *			   bridges in the encoder chain.
  * @bridge: bridge control structure
  *
- * Calls 'pre_enable' drm_bridge_funcs op for all the bridges in the encoder
+ * Calls ->pre_enable() &drm_bridge_funcs op for all the bridges in the encoder
  * chain, starting from the last bridge to the first. These are called
  * before calling the encoder's commit op.
  *
@@ -278,11 +261,11 @@ void drm_bridge_pre_enable(struct drm_bridge *bridge)
 EXPORT_SYMBOL(drm_bridge_pre_enable);
 
 /**
- * drm_bridge_enable - calls 'enable' drm_bridge_funcs op for all bridges
+ * drm_bridge_enable - calls ->enable() &drm_bridge_funcs op for all bridges
  *		       in the encoder chain.
  * @bridge: bridge control structure
  *
- * Calls 'enable' drm_bridge_funcs op for all the bridges in the encoder
+ * Calls ->enable() &drm_bridge_funcs op for all the bridges in the encoder
  * chain, starting from the first bridge to the last. These are called
  * after completing the encoder's commit op.
  *

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);
 };