drm/doc: Update drm_framebuffer docs

- Move the intro section into a DOC comment, and update it slightly.
- kernel-doc for struct drm_framebuffer!

v2:
- Copypaste fail (Sean).
- Explain the linear @offsets clearer (Ville).

Cc: Sean Paul <seanpaul@chromium.org>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471034937-651-12-git-send-email-daniel.vetter@ffwll.ch

Documentation/gpu/drm-kms.rst

@@ -39,30 +39,8 @@ Atomic Mode Setting Function Reference
 Frame Buffer Abstraction
 ========================
 
-Frame buffers are abstract memory objects that provide a source of
-pixels to scanout to a CRTC. Applications explicitly request the
-creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls
-and receive an opaque handle that can be passed to the KMS CRTC control,
-plane configuration and page flip functions.
-
-Frame buffers rely on the underneath memory manager for low-level memory
-operations. When creating a frame buffer applications pass a memory
-handle (or a list of memory handles for multi-planar formats) through
-the ``drm_mode_fb_cmd2`` argument. For drivers using GEM as their
-userspace buffer management interface this would be a GEM handle.
-Drivers are however free to use their own backing storage object
-handles, e.g. vmwgfx directly exposes special TTM handles to userspace
-and so expects TTM handles in the create ioctl and not GEM handles.
-
-The lifetime of a drm framebuffer is controlled with a reference count,
-drivers can grab additional references with
-:c:func:`drm_framebuffer_reference()`and drop them again with
-:c:func:`drm_framebuffer_unreference()`. For driver-private
-framebuffers for which the last reference is never dropped (e.g. for the
-fbdev framebuffer when the struct :c:type:`struct drm_framebuffer
-<drm_framebuffer>` is embedded into the fbdev helper struct)
-drivers can manually clean up a framebuffer at module unload time with
-:c:func:`drm_framebuffer_unregister_private()`.
+.. kernel-doc:: drivers/gpu/drm/drm_framebuffer.c
+   :doc: overview
 
 Frame Buffer Functions Reference
 --------------------------------

drivers/gpu/drm/drm_framebuffer.c

@@ -27,6 +27,41 @@
 
 #include "drm_crtc_internal.h"
 
+/**
+ * DOC: overview
+ *
+ * Frame buffers are abstract memory objects that provide a source of pixels to
+ * scanout to a CRTC. Applications explicitly request the creation of frame
+ * buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls and receive an opaque
+ * handle that can be passed to the KMS CRTC control, plane configuration and
+ * page flip functions.
+ *
+ * Frame buffers rely on the underlying memory manager for allocating backing
+ * storage. When creating a frame buffer applications pass a memory handle
+ * (or a list of memory handles for multi-planar formats) through the
+ * struct &drm_mode_fb_cmd2 argument. For drivers using GEM as their userspace
+ * buffer management interface this would be a GEM handle.  Drivers are however
+ * free to use their own backing storage object handles, e.g. vmwgfx directly
+ * exposes special TTM handles to userspace and so expects TTM handles in the
+ * create ioctl and not GEM handles.
+ *
+ * Framebuffers are tracked with struct &drm_framebuffer. They are published
+ * using drm_framebuffer_init() - after calling that function userspace can use
+ * and access the framebuffer object. The helper function
+ * drm_helper_mode_fill_fb_struct() can be used to pre-fill the required
+ * metadata fields.
+ *
+ * The lifetime of a drm framebuffer is controlled with a reference count,
+ * drivers can grab additional references with drm_framebuffer_reference() and
+ * drop them again with drm_framebuffer_unreference(). For driver-private
+ * framebuffers for which the last reference is never dropped (e.g. for the
+ * fbdev framebuffer when the struct struct &drm_framebuffer is embedded into
+ * the fbdev helper struct) drivers can manually clean up a framebuffer at
+ * module unload time with drm_framebuffer_unregister_private(). But doing this
+ * is not recommended, and it's better to have a normal free-standing struct
+ * &drm_framebuffer.
+ */
+
 /**
  * drm_mode_addfb - add an FB to the graphics configuration
  * @dev: drm device for the ioctl

include/drm/drm_framebuffer.h

@@ -92,37 +92,117 @@ struct drm_framebuffer_funcs {
 		     unsigned num_clips);
 };
 
-struct drm_framebuffer {
-	struct drm_device *dev;
-	/*
+/**
+ * struct drm_framebuffer - frame buffer object
+ *
  * Note that the fb is refcounted for the benefit of driver internals,
  * for example some hw, disabling a CRTC/plane is asynchronous, and
  * scanout does not actually complete until the next vblank.  So some
  * cleanup (like releasing the reference(s) on the backing GEM bo(s))
  * should be deferred.  In cases like this, the driver would like to
  * hold a ref to the fb even though it has already been removed from
-	 * userspace perspective.
-	 * The refcount is stored inside the mode object.
+ * userspace perspective. See drm_framebuffer_reference() and
+ * drm_framebuffer_unreference().
+ *
+ * The refcount is stored inside the mode object @base.
  */
-	/*
-	 * Place on the dev->mode_config.fb_list, access protected by
+struct drm_framebuffer {
+	/**
+	 * @dev: DRM device this framebuffer belongs to
+	 */
+	struct drm_device *dev;
+	/**
+	 * @head: Place on the dev->mode_config.fb_list, access protected by
 	 * dev->mode_config.fb_lock.
 	 */
 	struct list_head head;
+
+	/**
+	 * @base: base modeset object structure, contains the reference count.
+	 */
 	struct drm_mode_object base;
+	/**
+	 * @funcs: framebuffer vfunc table
+	 */
 	const struct drm_framebuffer_funcs *funcs;
+	/**
+	 * @pitches: Line stride per buffer. For userspace created object this
+	 * is copied from drm_mode_fb_cmd2.
+	 */
 	unsigned int pitches[4];
+	/**
+	 * @offsets: Offset from buffer start to the actual pixel data in bytes,
+	 * per buffer. For userspace created object this is copied from
+	 * drm_mode_fb_cmd2.
+	 *
+	 * Note that this is a linear offset and does not take into account
+	 * tiling or buffer laytou per @modifier. It meant to be used when the
+	 * actual pixel data for this framebuffer plane starts at an offset,
+	 * e.g.  when multiple planes are allocated within the same backing
+	 * storage buffer object. For tiled layouts this generally means it
+	 * @offsets must at least be tile-size aligned, but hardware often has
+	 * stricter requirements.
+	 *
+	 * This should not be used to specifiy x/y pixel offsets into the buffer
+	 * data (even for linear buffers). Specifying an x/y pixel offset is
+	 * instead done through the source rectangle in struct &drm_plane_state.
+	 */
 	unsigned int offsets[4];
+	/**
+	 * @modifier: Data layout modifier, per buffer. This is used to describe
+	 * tiling, or also special layouts (like compression) of auxiliary
+	 * buffers. For userspace created object this is copied from
+	 * drm_mode_fb_cmd2.
+	 */
 	uint64_t modifier[4];
+	/**
+	 * @width: Logical width of the visible area of the framebuffer, in
+	 * pixels.
+	 */
 	unsigned int width;
+	/**
+	 * @height: Logical height of the visible area of the framebuffer, in
+	 * pixels.
+	 */
 	unsigned int height;
-	/* depth can be 15 or 16 */
+	/**
+	 * @depth: Depth in bits per pixel for RGB formats. 0 for everything
+	 * else. Legacy information derived from @pixel_format, it's suggested to use
+	 * the DRM FOURCC codes and helper functions directly instead.
+	 */
 	unsigned int depth;
+	/**
+	 * @bits_per_pixel: Storage used bits per pixel for RGB formats. 0 for
+	 * everything else. Legacy information derived from @pixel_format, it's
+	 * suggested to use the DRM FOURCC codes and helper functions directly
+	 * instead.
+	 */
 	int bits_per_pixel;
+	/**
+	 * @flags: Framebuffer flags like DRM_MODE_FB_INTERLACED or
+	 * DRM_MODE_FB_MODIFIERS.
+	 */
 	int flags;
+	/**
+	 * @pixel_format: DRM FOURCC code describing the pixel format.
+	 */
 	uint32_t pixel_format; /* fourcc format */
+	/**
+	 * @hot_x: X coordinate of the cursor hotspot. Used by the legacy cursor
+	 * IOCTL when the driver supports cursor through a DRM_PLANE_TYPE_CURSOR
+	 * universal plane.
+	 */
 	int hot_x;
+	/**
+	 * @hot_y: Y coordinate of the cursor hotspot. Used by the legacy cursor
+	 * IOCTL when the driver supports cursor through a DRM_PLANE_TYPE_CURSOR
+	 * universal plane.
+	 */
 	int hot_y;
+	/**
+	 * @filp_head: Placed on struct &drm_file fbs list_head, protected by
+	 * fbs_lock in the same structure.
+	 */
 	struct list_head filp_head;
 };