drm/irq: kerneldoc polish

- Integrate into the drm DocBook
- Disable kerneldoc for functions not exported to drivers.
- Properly document the new drm_vblank_on|off and add cautious
  comments explaining when drm_vblank_pre|post_modesets shouldn't be
  used.
- General polish and OCD.

v2: Polish as suggested by Thierry.

Cc: Thierry Reding <thierry.reding@gmail.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Documentation/DocBook/drm.tmpl

@@ -2519,6 +2519,10 @@ void (*disable_vblank) (struct drm_device *dev, int crtc);</synopsis>
       with a call to <function>drm_vblank_cleanup</function> in the driver
       <methodname>unload</methodname> operation handler.
     </para>
+    <sect2>
+      <title>Vertical Blanking and Interrupt Handling Functions Reference</title>
+!Edrivers/gpu/drm/drm_irq.c
+    </sect2>
   </sect1>
 
   <!-- Internals: open/close, file operations and ioctls -->
@@ -2871,7 +2875,6 @@ int num_ioctls;</synopsis>
             </listitem>
           </varlistentry>
         </variablelist>
-<!--!Edrivers/char/drm/drm_irq.c-->
       </para>
     </sect1>
 

drivers/gpu/drm/drm_irq.c

-/**
- * \file drm_irq.c
- * IRQ support
+/*
+ * drm_irq.c IRQ and vblank support
  *
  * \author Rickard E. (Rik) Faith <faith@valinux.com>
  * \author Gareth Hughes <gareth@valinux.com>
@@ -156,6 +155,12 @@ static void vblank_disable_fn(unsigned long arg)
 	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
 }
 
+/**
+ * drm_vblank_cleanup - cleanup vblank support
+ * @dev: DRM device
+ *
+ * This function cleans up any resources allocated in drm_vblank_init.
+ */
 void drm_vblank_cleanup(struct drm_device *dev)
 {
 	int crtc;
@@ -175,6 +180,16 @@ void drm_vblank_cleanup(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_vblank_cleanup);
 
+/**
+ * drm_vblank_init - initialize vblank support
+ * @dev: drm_device
+ * @num_crtcs: number of crtcs supported by @dev
+ *
+ * This function initializes vblank support for @num_crtcs display pipelines.
+ *
+ * Returns:
+ * Zero on success or a negative error code on failure.
+ */
 int drm_vblank_init(struct drm_device *dev, int num_crtcs)
 {
 	int i, ret = -ENOMEM;
@@ -238,13 +253,21 @@ static void drm_irq_vgaarb_nokms(void *cookie, bool state)
 }
 
 /**
- * Install IRQ handler.
- *
- * \param dev DRM device.
+ * drm_irq_install - install IRQ handler
+ * @dev: DRM device
+ * @irq: IRQ number to install the handler for
  *
  * Initializes the IRQ related data. Installs the handler, calling the driver
- * \c irq_preinstall() and \c irq_postinstall() functions
- * before and after the installation.
+ * irq_preinstall() and irq_postinstall() functions before and after the
+ * installation.
+ *
+ * This is the simplified helper interface provided for drivers with no special
+ * needs. Drivers which need to install interrupt handlers for multiple
+ * interrupts must instead set drm_device->irq_enabled to signal the DRM core
+ * that vblank interrupts are available.
+ *
+ * Returns:
+ * Zero on success or a negative error code on failure.
  */
 int drm_irq_install(struct drm_device *dev, int irq)
 {
@@ -304,11 +327,20 @@ int drm_irq_install(struct drm_device *dev, int irq)
 EXPORT_SYMBOL(drm_irq_install);
 
 /**
- * Uninstall the IRQ handler.
+ * drm_irq_uninstall - uninstall the IRQ handler
+ * @dev: DRM device
+ *
+ * Calls the driver's irq_uninstall() function and unregisters the IRQ handler.
+ * This should only be called by drivers which used drm_irq_install() to set up
+ * their interrupt handler. Other drivers must only reset
+ * drm_device->irq_enabled to false.
  *
- * \param dev DRM device.
+ * Note that for kernel modesetting drivers it is a bug if this function fails.
+ * The sanity checks are only to catch buggy user modesetting drivers which call
+ * the same function through an ioctl.
  *
- * Calls the driver's \c irq_uninstall() function, and stops the irq.
+ * Returns:
+ * Zero on success or a negative error code on failure.
  */
 int drm_irq_uninstall(struct drm_device *dev)
 {
@@ -353,7 +385,7 @@ int drm_irq_uninstall(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_irq_uninstall);
 
-/**
+/*
  * IRQ control ioctl.
  *
  * \param inode device inode.
@@ -406,15 +438,14 @@ int drm_control(struct drm_device *dev, void *data,
 }
 
 /**
- * drm_calc_timestamping_constants - Calculate vblank timestamp constants
- *
- * @crtc drm_crtc whose timestamp constants should be updated.
- * @mode display mode containing the scanout timings
+ * drm_calc_timestamping_constants - calculate vblank timestamp constants
+ * @crtc: drm_crtc whose timestamp constants should be updated.
+ * @mode: display mode containing the scanout timings
  *
  * Calculate and store various constants which are later
  * needed by vblank and swap-completion timestamping, e.g,
  * by drm_calc_vbltimestamp_from_scanoutpos(). They are
- * derived from crtc's true scanout timing, so they take
+ * derived from CRTC's true scanout timing, so they take
  * things like panel scaling or other adjustments into account.
  */
 void drm_calc_timestamping_constants(struct drm_crtc *crtc,
@@ -459,11 +490,22 @@ void drm_calc_timestamping_constants(struct drm_crtc *crtc,
 EXPORT_SYMBOL(drm_calc_timestamping_constants);
 
 /**
- * drm_calc_vbltimestamp_from_scanoutpos - helper routine for kms
- * drivers. Implements calculation of exact vblank timestamps from
- * given drm_display_mode timings and current video scanout position
- * of a crtc. This can be called from within get_vblank_timestamp()
- * implementation of a kms driver to implement the actual timestamping.
+ * drm_calc_vbltimestamp_from_scanoutpos - precise vblank timestamp helper
+ * @dev: DRM device
+ * @crtc: Which CRTC's vblank timestamp to retrieve
+ * @max_error: Desired maximum allowable error in timestamps (nanosecs)
+ *             On return contains true maximum error of timestamp
+ * @vblank_time: Pointer to struct timeval which should receive the timestamp
+ * @flags: Flags to pass to driver:
+ *         0 = Default,
+ *         DRM_CALLED_FROM_VBLIRQ = If function is called from vbl IRQ handler
+ * @refcrtc: CRTC which defines scanout timing
+ * @mode: mode which defines the scanout timings
+ *
+ * Implements calculation of exact vblank timestamps from given drm_display_mode
+ * timings and current video scanout position of a CRTC. This can be called from
+ * within get_vblank_timestamp() implementation of a kms driver to implement the
+ * actual timestamping.
  *
  * Should return timestamps conforming to the OML_sync_control OpenML
  * extension specification. The timestamp corresponds to the end of
@@ -478,21 +520,11 @@ EXPORT_SYMBOL(drm_calc_timestamping_constants);
  * returns as no operation if a doublescan or interlaced video mode is
  * active. Higher level code is expected to handle this.
  *
- * @dev: DRM device.
- * @crtc: Which crtc's vblank timestamp to retrieve.
- * @max_error: Desired maximum allowable error in timestamps (nanosecs).
- *             On return contains true maximum error of timestamp.
- * @vblank_time: Pointer to struct timeval which should receive the timestamp.
- * @flags: Flags to pass to driver:
- *         0 = Default.
- *         DRM_CALLED_FROM_VBLIRQ = If function is called from vbl irq handler.
- * @refcrtc: drm_crtc* of crtc which defines scanout timing.
- * @mode: mode which defines the scanout timings
- *
- * Returns negative value on error, failure or if not supported in current
+ * Returns:
+ * Negative value on error, failure or if not supported in current
  * video mode:
  *
- * -EINVAL   - Invalid crtc.
+ * -EINVAL   - Invalid CRTC.
  * -EAGAIN   - Temporary unavailable, e.g., called before initial modeset.
  * -ENOTSUPP - Function not supported in current display mode.
  * -EIO      - Failed, e.g., due to failed scanout position query.
@@ -641,23 +673,23 @@ static struct timeval get_drm_timestamp(void)
 
 /**
  * drm_get_last_vbltimestamp - retrieve raw timestamp for the most recent
- * vblank interval.
- *
+ * 			       vblank interval
  * @dev: DRM device
- * @crtc: which crtc's vblank timestamp to retrieve
+ * @crtc: which CRTC's vblank timestamp to retrieve
  * @tvblank: Pointer to target struct timeval which should receive the timestamp
  * @flags: Flags to pass to driver:
- *         0 = Default.
- *         DRM_CALLED_FROM_VBLIRQ = If function is called from vbl irq handler.
+ *         0 = Default,
+ *         DRM_CALLED_FROM_VBLIRQ = If function is called from vbl IRQ handler
  *
  * Fetches the system timestamp corresponding to the time of the most recent
- * vblank interval on specified crtc. May call into kms-driver to
+ * vblank interval on specified CRTC. May call into kms-driver to
  * compute the timestamp with a high-precision GPU specific method.
  *
  * Returns zero if timestamp originates from uncorrected do_gettimeofday()
  * call, i.e., it isn't very precisely locked to the true vblank.
  *
- * Returns non-zero if timestamp is considered to be very precise.
+ * Returns:
+ * Non-zero if timestamp is considered to be very precise, zero otherwise.
  */
 u32 drm_get_last_vbltimestamp(struct drm_device *dev, int crtc,
 			      struct timeval *tvblank, unsigned flags)
@@ -692,6 +724,9 @@ EXPORT_SYMBOL(drm_get_last_vbltimestamp);
  * Fetches the "cooked" vblank count value that represents the number of
  * vblank events since the system was booted, including lost events due to
  * modesetting activity.
+ *
+ * Returns:
+ * The software vblank counter.
  */
 u32 drm_vblank_count(struct drm_device *dev, int crtc)
 {
@@ -710,8 +745,7 @@ EXPORT_SYMBOL(drm_vblank_count);
  * Fetches the "cooked" vblank count value that represents the number of
  * vblank events since the system was booted, including lost events due to
  * modesetting activity. Returns corresponding system timestamp of the time
- * of the vblank interval that corresponds to the current value vblank counter
- * value.
+ * of the vblank interval that corresponds to the current vblank counter value.
  */
 u32 drm_vblank_count_and_time(struct drm_device *dev, int crtc,
 			      struct timeval *vblanktime)
@@ -882,7 +916,7 @@ static int drm_vblank_enable(struct drm_device *dev, int crtc)
  * Acquire a reference count on vblank events to avoid having them disabled
  * while in use.
  *
- * RETURNS
+ * Returns:
  * Zero on success, nonzero on failure.
  */
 int drm_vblank_get(struct drm_device *dev, int crtc)
@@ -930,6 +964,13 @@ EXPORT_SYMBOL(drm_vblank_put);
  * drm_vblank_off - disable vblank events on a CRTC
  * @dev: DRM device
  * @crtc: CRTC in question
+ *
+ * Drivers can use this function to shut down the vblank interrupt handling when
+ * disabling a crtc. This function ensures that the latest vblank frame count is
+ * stored so that drm_vblank_on() can restore it again.
+ *
+ * Drivers must use this function when the hardware vblank counter can get
+ * reset, e.g. when suspending.
  */
 void drm_vblank_off(struct drm_device *dev, int crtc)
 {
@@ -966,6 +1007,11 @@ EXPORT_SYMBOL(drm_vblank_off);
  * drm_vblank_on - enable vblank events on a CRTC
  * @dev: DRM device
  * @crtc: CRTC in question
+ *
+ * This functions restores the vblank interrupt state captured with
+ * drm_vblank_off() again. Note that calls to drm_vblank_on() and
+ * drm_vblank_off() can be unbalanced and so can also be unconditionaly called
+ * in driver load code to reflect the current hardware state of the crtc.
  */
 void drm_vblank_on(struct drm_device *dev, int crtc)
 {
@@ -986,6 +1032,21 @@ EXPORT_SYMBOL(drm_vblank_on);
  *
  * Account for vblank events across mode setting events, which will likely
  * reset the hardware frame counter.
+ *
+ * This is done by grabbing a temporary vblank reference to ensure that the
+ * vblank interrupt keeps running across the modeset sequence. With this the
+ * software-side vblank frame counting will ensure that there are no jumps or
+ * discontinuities.
+ *
+ * Unfortunately this approach is racy and also doesn't work when the vblank
+ * interrupt stops running, e.g. across system suspend resume. It is therefore
+ * highly recommended that drivers use the newer drm_vblank_off() and
+ * drm_vblank_on() instead. drm_vblank_pre_modeset() only works correctly when
+ * using "cooked" software vblank frame counters and not relying on any hardware
+ * counters.
+ *
+ * Drivers must call drm_vblank_post_modeset() when re-enabling the same crtc
+ * again.
  */
 void drm_vblank_pre_modeset(struct drm_device *dev, int crtc)
 {
@@ -1007,6 +1068,14 @@ void drm_vblank_pre_modeset(struct drm_device *dev, int crtc)
 }
 EXPORT_SYMBOL(drm_vblank_pre_modeset);
 
+/**
+ * drm_vblank_post_modeset - undo drm_vblank_pre_modeset changes
+ * @dev: DRM device
+ * @crtc: CRTC in question
+ *
+ * This function again drops the temporary vblank reference acquired in
+ * drm_vblank_pre_modeset.
+ */
 void drm_vblank_post_modeset(struct drm_device *dev, int crtc)
 {
 	unsigned long irqflags;
@@ -1028,7 +1097,7 @@ void drm_vblank_post_modeset(struct drm_device *dev, int crtc)
 }
 EXPORT_SYMBOL(drm_vblank_post_modeset);
 
-/**
+/*
  * drm_modeset_ctl - handle vblank event counter changes across mode switch
  * @DRM_IOCTL_ARGS: standard ioctl arguments
  *
@@ -1141,7 +1210,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, int pipe,
 	return ret;
 }
 
-/**
+/*
  * Wait for VBLANK.
  *
  * \param inode device inode.
@@ -1152,7 +1221,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, int pipe,
  *
  * This function enables the vblank interrupt on the pipe requested, then
  * sleeps waiting for the requested sequence number to occur, and drops
- * the vblank interrupt refcount afterwards. (vblank irq disable follows that
+ * the vblank interrupt refcount afterwards. (vblank IRQ disable follows that
  * after a timeout with no further vblank waits scheduled).
  */
 int drm_wait_vblank(struct drm_device *dev, void *data,