drm/doc: Document drm_file.[hc]

Well, mostly drm_file.h, and clean up all related things:

- I didnt' figure out the difference between preclose and postclose.
  The existing explanation in drm-internals.rst didn't convince me,
  since it's also really outdated - we clean up pending DRM events in
  the core nowadays. I put a FIXME in for the future.

- Another FIXME is to have a macro for default fops.

- Lots of links all around, main areas are to tie the overview in
  drm_file.c more into the callbacks in struct drm_device, and the
  other is to link render/primary node code to the right sections in
  drm-uapi.rst.

- Also moved the open/close stuff to drm_drv.h from drm-internals.rst,
  seems like the better place for that information. Since that section
  was rather outdated this amounted to full-on rewrite.

A big missing piece here is some overview graph, but I think better to
wait with that one until drm_device and drm_driver are also fully
documented.

v2: Nits from Sean.

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170308141257.12119-12-daniel.vetter@ffwll.ch

2 files changed, 315 insertions, 31 deletions

diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index 4321d012c4ba..8f900fb30275 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -64,7 +64,6 @@ struct drm_mode_create_dumb;
  * structure for GEM drivers.
  */
 struct drm_driver {
-
 	/**
 	 * @load:
 	 *
@@ -76,14 +75,94 @@ struct drm_driver {
 	 * See drm_dev_init() and drm_dev_register() for proper and
 	 * race-free way to set up a &struct drm_device.
 	 *
+	 * This is deprecated, do not use!
+	 *
 	 * Returns:
 	 *
 	 * Zero on success, non-zero value on failure.
 	 */
 	int (*load) (struct drm_device *, unsigned long flags);
+
+	/**
+	 * @open:
+	 *
+	 * Driver callback when a new &struct drm_file is opened. Useful for
+	 * setting up driver-private data structures like buffer allocators,
+	 * execution contexts or similar things. Such driver-private resources
+	 * must be released again in @postclose.
+	 *
+	 * Since the display/modeset side of DRM can only be owned by exactly
+	 * one &struct drm_file (see &drm_file.is_master and &drm_device.master)
+	 * there should never be a need to set up any modeset related resources
+	 * in this callback. Doing so would be a driver design bug.
+	 *
+	 * Returns:
+	 *
+	 * 0 on success, a negative error code on failure, which will be
+	 * promoted to userspace as the result of the open() system call.
+	 */
 	int (*open) (struct drm_device *, struct drm_file *);
+
+	/**
+	 * @preclose:
+	 *
+	 * One of the driver callbacks when a new &struct drm_file is closed.
+	 * Useful for tearing down driver-private data structures allocated in
+	 * @open like buffer allocators, execution contexts or similar things.
+	 *
+	 * Since the display/modeset side of DRM can only be owned by exactly
+	 * one &struct drm_file (see &drm_file.is_master and &drm_device.master)
+	 * there should never be a need to tear down any modeset related
+	 * resources in this callback. Doing so would be a driver design bug.
+	 *
+	 * FIXME: It is not really clear why there's both @preclose and
+	 * @postclose. Without a really good reason, use @postclose only.
+	 */
 	void (*preclose) (struct drm_device *, struct drm_file *file_priv);
+
+	/**
+	 * @postclose:
+	 *
+	 * One of the driver callbacks when a new &struct drm_file is closed.
+	 * Useful for tearing down driver-private data structures allocated in
+	 * @open like buffer allocators, execution contexts or similar things.
+	 *
+	 * Since the display/modeset side of DRM can only be owned by exactly
+	 * one &struct drm_file (see &drm_file.is_master and &drm_device.master)
+	 * there should never be a need to tear down any modeset related
+	 * resources in this callback. Doing so would be a driver design bug.
+	 *
+	 * FIXME: It is not really clear why there's both @preclose and
+	 * @postclose. Without a really good reason, use @postclose only.
+	 */
 	void (*postclose) (struct drm_device *, struct drm_file *);
+
+	/**
+	 * @lastclose:
+	 *
+	 * Called when the last &struct drm_file has been closed and there's
+	 * currently no userspace client for the &struct drm_device.
+	 *
+	 * Modern drivers should only use this to force-restore the fbdev
+	 * framebuffer using drm_fb_helper_restore_fbdev_mode_unlocked().
+	 * Anything else would indicate there's something seriously wrong.
+	 * Modern drivers can also use this to execute delayed power switching
+	 * state changes, e.g. in conjunction with the :ref:`vga_switcheroo`
+	 * infrastructure.
+	 *
+	 * This is called after @preclose and @postclose have been called.
+	 *
+	 * NOTE:
+	 *
+	 * All legacy drivers use this callback to de-initialize the hardware.
+	 * This is purely because of the shadow-attach model, where the DRM
+	 * kernel driver does not really own the hardware. Instead ownershipe is
+	 * handled with the help of userspace through an inheritedly racy dance
+	 * to set/unset the VT into raw mode.
+	 *
+	 * Legacy drivers initialize the hardware in the @firstopen callback,
+	 * which isn't even called for modern drivers.
+	 */
 	void (*lastclose) (struct drm_device *);
 
 	/**
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 4e347399a7bd..5dd27ae5c47c 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -45,6 +45,7 @@ struct drm_device;
  * FIXME: Not sure we want to have drm_minor here in the end, but to avoid
  * header include loops we need it here for now.
  */
+
 enum drm_minor_type {
 	DRM_MINOR_PRIMARY,
 	DRM_MINOR_CONTROL,
@@ -52,12 +53,19 @@ enum drm_minor_type {
 };
 
 /**
- * DRM minor structure. This structure represents a drm minor number.
+ * struct drm_minor - DRM device minor structure
+ *
+ * This structure represents a DRM minor number for device nodes in /dev.
+ * Entirely opaque to drivers and should never be inspected directly by drivers.
+ * Drivers instead should only interact with &struct drm_file and of course
+ * &struct drm_device, which is also where driver-private data and resources can
+ * be attached to.
  */
 struct drm_minor {
-	int index;			/**< Minor device number */
-	int type;                       /**< Control or render */
-	struct device *kdev;		/**< Linux device */
+	/* private: */
+	int index;			/* Minor device number */
+	int type;                       /* Control or render */
+	struct device *kdev;		/* Linux device */
 	struct drm_device *dev;
 
 	struct dentry *debugfs_root;
@@ -66,89 +74,286 @@ struct drm_minor {
 	struct mutex debugfs_lock; /* Protects debugfs_list. */
 };
 
-/* Event queued up for userspace to read */
+/**
+ * struct drm_pending_event - Event queued up for userspace to read
+ *
+ * This represents a DRM event. Drivers can use this as a generic completion
+ * mechanism, which supports kernel-internal &struct completion, &struct dma_fence
+ * and also the DRM-specific &struct drm_event delivery mechanism.
+ */
 struct drm_pending_event {
+	/**
+	 * @completion:
+	 *
+	 * Optional pointer to a kernel internal completion signalled when
+	 * drm_send_event() is called, useful to internally synchronize with
+	 * nonblocking operations.
+	 */
 	struct completion *completion;
+
+	/**
+	 * @completion_release:
+	 *
+	 * Optional callback currently only used by the atomic modeset helpers
+	 * to clean up the reference count for the structure @completion is
+	 * stored in.
+	 */
 	void (*completion_release)(struct completion *completion);
+
+	/**
+	 * @event:
+	 *
+	 * Pointer to the actual event that should be sent to userspace to be
+	 * read using drm_read(). Can be optional, since nowadays events are
+	 * also used to signal kernel internal threads with @completion or DMA
+	 * transactions using @fence.
+	 */
 	struct drm_event *event;
+
+	/**
+	 * @fence:
+	 *
+	 * Optional DMA fence to unblock other hardware transactions which
+	 * depend upon the nonblocking DRM operation this event represents.
+	 */
 	struct dma_fence *fence;
+
+	/**
+	 * @file_priv:
+	 *
+	 * &struct drm_file where @event should be delivered to. Only set when
+	 * @event is set.
+	 */
+	struct drm_file *file_priv;
+
+	/**
+	 * @link:
+	 *
+	 * Double-linked list to keep track of this event. Can be used by the
+	 * driver up to the point when it calls drm_send_event(), after that
+	 * this list entry is owned by the core for its own book-keeping.
+	 */
 	struct list_head link;
+
+	/**
+	 * @pending_link:
+	 *
+	 * Entry on &drm_file.pending_event_list, to keep track of all pending
+	 * events for @file_priv, to allow correct unwinding of them when
+	 * userspace closes the file before the event is delivered.
+	 */
 	struct list_head pending_link;
-	struct drm_file *file_priv;
 };
 
-/** File private data */
+/**
+ * struct drm_file - DRM file private data
+ *
+ * This structure tracks DRM state per open file descriptor.
+ */
 struct drm_file {
+	/**
+	 * @authenticated:
+	 *
+	 * Whether the client is allowed to submit rendering, which for legacy
+	 * nodes means it must be authenticated.
+	 *
+	 * See also the :ref:`section on primary nodes and authentication
+	 * <drm_primary_node>`.
+	 */
 	unsigned authenticated :1;
-	/* true when the client has asked us to expose stereo 3D mode flags */
+
+	/**
+	 * @stereo_allowed:
+	 *
+	 * True when the client has asked us to expose stereo 3D mode flags.
+	 */
 	unsigned stereo_allowed :1;
-	/*
-	 * true if client understands CRTC primary planes and cursor planes
-	 * in the plane list
+
+	/**
+	 * @universal_planes:
+	 *
+	 * True if client understands CRTC primary planes and cursor planes
+	 * in the plane list. Automatically set when @atomic is set.
 	 */
 	unsigned universal_planes:1;
-	/* true if client understands atomic properties */
+
+	/** @atomic: True if client understands atomic properties. */
 	unsigned atomic:1;
-	/*
-	 * This client is the creator of @master.
-	 * Protected by struct drm_device::master_mutex.
+
+	/**
+	 * @is_master:
+	 *
+	 * This client is the creator of @master. Protected by struct
+	 * &drm_device.master_mutex.
+	 *
+	 * See also the :ref:`section on primary nodes and authentication
+	 * <drm_primary_node>`.
 	 */
 	unsigned is_master:1;
 
+	/**
+	 * @master:
+	 *
+	 * Master this node is currently associated with. Only relevant if
+	 * drm_is_primary_client() returns true. Note that this only
+	 * matches &drm_device.master if the master is the currently active one.
+	 *
+	 * See also @authentication and @is_master and the :ref:`section on
+	 * primary nodes and authentication <drm_primary_node>`.
+	 */
+	struct drm_master *master;
+
+	/** @pid: Process that opened this file. */
 	struct pid *pid;
+
+	/** @magic: Authentication magic, see @authenticated. */
 	drm_magic_t magic;
+
+	/**
+	 * @lhead:
+	 *
+	 * List of all open files of a DRM device, linked into
+	 * &drm_device.filelist. Protected by &drm_device.filelist_mutex.
+	 */
 	struct list_head lhead;
+
+	/** @minor: &struct drm_minor for this file. */
 	struct drm_minor *minor;
-	unsigned long lock_count;
 
-	/** Mapping of mm object handles to object pointers. */
+	/**
+	 * @object_idr:
+	 *
+	 * Mapping of mm object handles to object pointers. Used by the GEM
+	 * subsystem. Protected by @table_lock.
+	 */
 	struct idr object_idr;
-	/** Lock for synchronization of access to object_idr. */
+
+	/** @table_lock: Protects @object_idr. */
 	spinlock_t table_lock;
 
+	/** @filp: Pointer to the core file structure. */
 	struct file *filp;
+
+	/**
+	 * @driver_priv:
+	 *
+	 * Optional pointer for driver private data. Can be allocated in
+	 * &drm_driver.open and should be freed in &drm_driver.postclose.
+	 */
 	void *driver_priv;
 
-	struct drm_master *master; /* master this node is currently associated with
-				      N.B. not always dev->master */
 	/**
-	 * fbs - List of framebuffers associated with this file.
+	 * @fbs:
+	 *
+	 * List of &struct drm_framebuffer associated with this file, using the
+	 * &drm_framebuffer.filp_head entry.
 	 *
-	 * Protected by fbs_lock. Note that the fbs list holds a reference on
-	 * the fb object to prevent it from untimely disappearing.
+	 * Protected by @fbs_lock. Note that the @fbs list holds a reference on
+	 * the framebuffer object to prevent it from untimely disappearing.
 	 */
 	struct list_head fbs;
+
+	/** @fbs_lock: Protects @fbs. */
 	struct mutex fbs_lock;
 
-	/** User-created blob properties; this retains a reference on the
-	 *  property. */
+	/**
+	 * @blobs:
+	 *
+	 * User-created blob properties; this retains a reference on the
+	 * property.
+	 *
+	 * Protected by @drm_mode_config.blob_lock;
+	 */
 	struct list_head blobs;
 
+	/** @event_wait: Waitqueue for new events added to @event_list. */
 	wait_queue_head_t event_wait;
+
+	/**
+	 * @pending_event_list:
+	 *
+	 * List of pending &struct drm_pending_event, used to clean up pending
+	 * events in case this file gets closed before the event is signalled.
+	 * Uses the &drm_pending_event.pending_link entry.
+	 *
+	 * Protect by &drm_device.event_lock.
+	 */
 	struct list_head pending_event_list;
+
+	/**
+	 * @event_list:
+	 *
+	 * List of &struct drm_pending_event, ready for delivery to userspace
+	 * through drm_read(). Uses the &drm_pending_event.link entry.
+	 *
+	 * Protect by &drm_device.event_lock.
+	 */
 	struct list_head event_list;
+
+	/**
+	 * @event_space:
+	 *
+	 * Available event space to prevent userspace from
+	 * exhausting kernel memory. Currently limited to the fairly arbitrary
+	 * value of 4KB.
+	 */
 	int event_space;
 
+	/** @event_read_lock: Serializes drm_read(). */
 	struct mutex event_read_lock;
 
+	/**
+	 * @prime:
+	 *
+	 * Per-file buffer caches used by the PRIME buffer sharing code.
+	 */
 	struct drm_prime_file_private prime;
+
+	/* private: */
+	unsigned long lock_count; /* DRI1 legacy lock count */
 };
 
+/**
+ * drm_is_primary_client - is this an open file of the primary node
+ * @file_priv: DRM file
+ *
+ * Returns true if this is an open file of the primary node, i.e.
+ * &drm_file.minor of @file_priv is a primary minor.
+ *
+ * See also the :ref:`section on primary nodes and authentication
+ * <drm_primary_node>`.
+ */
+static inline bool drm_is_primary_client(const struct drm_file *file_priv)
+{
+	return file_priv->minor->type == DRM_MINOR_PRIMARY;
+}
+
+/**
+ * drm_is_render_client - is this an open file of the render node
+ * @file_priv: DRM file
+ *
+ * Returns true if this is an open file of the render node, i.e.
+ * &drm_file.minor of @file_priv is a render minor.
+ *
+ * See also the :ref:`section on render nodes <drm_render_node>`.
+ */
 static inline bool drm_is_render_client(const struct drm_file *file_priv)
 {
 	return file_priv->minor->type == DRM_MINOR_RENDER;
 }
 
+/**
+ * drm_is_control_client - is this an open file of the control node
+ * @file_priv: DRM file
+ *
+ * Control nodes are deprecated and in the process of getting removed from the
+ * DRM userspace API. Do not ever use!
+ */
 static inline bool drm_is_control_client(const struct drm_file *file_priv)
 {
 	return file_priv->minor->type == DRM_MINOR_CONTROL;
 }
 
-static inline bool drm_is_primary_client(const struct drm_file *file_priv)
-{
-	return file_priv->minor->type == DRM_MINOR_PRIMARY;
-}
-
 int drm_open(struct inode *inode, struct file *filp);
 ssize_t drm_read(struct file *filp, char __user *buffer,
 		 size_t count, loff_t *offset);