drm/prime: Update docs

Yes this is a bit a big patch, but since it's essentially a complete
rewrite of all the prime docs I didn't see how to better split it up.

Changes:
- Consistently point to drm_gem_object_funcs as the preferred hooks,
  where applicable.

- Document all the hooks in &drm_driver that lacked kerneldoc.

- Completely new overview section, which now also includes the cleaned
  up lifetime/reference counting subchapter. I also mentioned the weak
  references in there due to the lookup caches.

- Completely rewritten helper intro section, highlight the
  import/export related functionality.

- Polish for all the functions and more cross references.

I also sprinkled a bunch of todos all over.

Most important: 0 code changes in here. The cleanup motivated by
reading and improving all this will follow later on.

v2: Actually update the prime helper docs. Plus add a few FIXMEs that
I won't address right away in subsequent cleanup patches.

v3:
- Split out the function moving. This patch is now exclusively
  documentation changes.
- Typos and nits (Sam).

v4: Polish suggestions from Noralf.
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Noralf Trønnes <noralf@tronnes.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Eric Anholt <eric@anholt.net>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190620124615.24434-1-daniel.vetter@ffwll.ch

Documentation/gpu/drm-mm.rst

@@ -433,43 +433,11 @@ PRIME is the cross device buffer sharing framework in drm, originally
 created for the OPTIMUS range of multi-gpu platforms. To userspace PRIME
 buffers are dma-buf based file descriptors.
 
-Overview and Driver Interface
------------------------------
+Overview and Lifetime Rules
+---------------------------
 
-Similar to GEM global names, PRIME file descriptors are also used to
-share buffer objects across processes. They offer additional security:
-as file descriptors must be explicitly sent over UNIX domain sockets to
-be shared between applications, they can't be guessed like the globally
-unique GEM names.
-
-Drivers that support the PRIME API must set the DRIVER_PRIME bit in the
-struct :c:type:`struct drm_driver <drm_driver>`
-driver_features field, and implement the prime_handle_to_fd and
-prime_fd_to_handle operations.
-
-int (\*prime_handle_to_fd)(struct drm_device \*dev, struct drm_file
-\*file_priv, uint32_t handle, uint32_t flags, int \*prime_fd); int
-(\*prime_fd_to_handle)(struct drm_device \*dev, struct drm_file
-\*file_priv, int prime_fd, uint32_t \*handle); Those two operations
-convert a handle to a PRIME file descriptor and vice versa. Drivers must
-use the kernel dma-buf buffer sharing framework to manage the PRIME file
-descriptors. Similar to the mode setting API PRIME is agnostic to the
-underlying buffer object manager, as long as handles are 32bit unsigned
-integers.
-
-While non-GEM drivers must implement the operations themselves, GEM
-drivers must use the :c:func:`drm_gem_prime_handle_to_fd()` and
-:c:func:`drm_gem_prime_fd_to_handle()` helper functions. Those
-helpers rely on the driver gem_prime_export and gem_prime_import
-operations to create a dma-buf instance from a GEM object (dma-buf
-exporter role) and to create a GEM object from a dma-buf instance
-(dma-buf importer role).
-
-struct dma_buf \* (\*gem_prime_export)(struct drm_device \*dev,
-struct drm_gem_object \*obj, int flags); struct drm_gem_object \*
-(\*gem_prime_import)(struct drm_device \*dev, struct dma_buf
-\*dma_buf); These two operations are mandatory for GEM drivers that
-support PRIME.
+.. kernel-doc:: drivers/gpu/drm/drm_prime.c
+   :doc: overview and lifetime rules
 
 PRIME Helper Functions
 ----------------------

include/drm/drm_drv.h

@@ -502,21 +502,25 @@ struct drm_driver {
 	 * @gem_free_object: deconstructor for drm_gem_objects
 	 *
 	 * This is deprecated and should not be used by new drivers. Use
-	 * @gem_free_object_unlocked instead.
+	 * &drm_gem_object_funcs.free instead.
 	 */
 	void (*gem_free_object) (struct drm_gem_object *obj);
 
 	/**
 	 * @gem_free_object_unlocked: deconstructor for drm_gem_objects
 	 *
-	 * This is for drivers which are not encumbered with &drm_device.struct_mutex
-	 * legacy locking schemes. Use this hook instead of @gem_free_object.
+	 * This is deprecated and should not be used by new drivers. Use
+	 * &drm_gem_object_funcs.free instead.
+	 * Compared to @gem_free_object this is not encumbered with
+	 * &drm_device.struct_mutex legacy locking schemes.
 	 */
 	void (*gem_free_object_unlocked) (struct drm_gem_object *obj);
 
 	/**
 	 * @gem_open_object:
 	 *
+	 * This callback is deprecated in favour of &drm_gem_object_funcs.open.
+	 *
 	 * Driver hook called upon gem handle creation
 	 */
 	int (*gem_open_object) (struct drm_gem_object *, struct drm_file *);
@@ -524,6 +528,8 @@ struct drm_driver {
 	/**
 	 * @gem_close_object:
 	 *
+	 * This callback is deprecated in favour of &drm_gem_object_funcs.close.
+	 *
 	 * Driver hook called upon gem handle release
 	 */
 	void (*gem_close_object) (struct drm_gem_object *, struct drm_file *);
@@ -531,6 +537,9 @@ struct drm_driver {
 	/**
 	 * @gem_print_info:
 	 *
+	 * This callback is deprecated in favour of
+	 * &drm_gem_object_funcs.print_info.
+	 *
 	 * If driver subclasses struct &drm_gem_object, it can implement this
 	 * optional hook for printing additional driver specific info.
 	 *
@@ -545,56 +554,120 @@ struct drm_driver {
 	/**
 	 * @gem_create_object: constructor for gem objects
 	 *
-	 * Hook for allocating the GEM object struct, for use by core
-	 * helpers.
+	 * Hook for allocating the GEM object struct, for use by the CMA and
+	 * SHMEM GEM helpers.
 	 */
 	struct drm_gem_object *(*gem_create_object)(struct drm_device *dev,
 						    size_t size);
-
-	/* prime: */
 	/**
 	 * @prime_handle_to_fd:
 	 *
-	 * export handle -> fd (see drm_gem_prime_handle_to_fd() helper)
+	 * Main PRIME export function. Should be implemented with
+	 * drm_gem_prime_handle_to_fd() for GEM based drivers.
+	 *
+	 * For an in-depth discussion see :ref:`PRIME buffer sharing
+	 * documentation <prime_buffer_sharing>`.
 	 */
 	int (*prime_handle_to_fd)(struct drm_device *dev, struct drm_file *file_priv,
 				uint32_t handle, uint32_t flags, int *prime_fd);
 	/**
 	 * @prime_fd_to_handle:
 	 *
-	 * import fd -> handle (see drm_gem_prime_fd_to_handle() helper)
+	 * Main PRIME import function. Should be implemented with
+	 * drm_gem_prime_fd_to_handle() for GEM based drivers.
+	 *
+	 * For an in-depth discussion see :ref:`PRIME buffer sharing
+	 * documentation <prime_buffer_sharing>`.
 	 */
 	int (*prime_fd_to_handle)(struct drm_device *dev, struct drm_file *file_priv,
 				int prime_fd, uint32_t *handle);
 	/**
 	 * @gem_prime_export:
 	 *
-	 * export GEM -> dmabuf
-	 *
-	 * This defaults to drm_gem_prime_export() if not set.
+	 * Export hook for GEM drivers. Deprecated in favour of
+	 * &drm_gem_object_funcs.export.
 	 */
 	struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
 				struct drm_gem_object *obj, int flags);
 	/**
 	 * @gem_prime_import:
 	 *
-	 * import dmabuf -> GEM
+	 * Import hook for GEM drivers.
 	 *
 	 * This defaults to drm_gem_prime_import() if not set.
 	 */
 	struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev,
 				struct dma_buf *dma_buf);
+
+	/**
+	 * @gem_prime_pin:
+	 *
+	 * Deprecated hook in favour of &drm_gem_object_funcs.pin.
+	 */
 	int (*gem_prime_pin)(struct drm_gem_object *obj);
+
+	/**
+	 * @gem_prime_unpin:
+	 *
+	 * Deprecated hook in favour of &drm_gem_object_funcs.unpin.
+	 */
 	void (*gem_prime_unpin)(struct drm_gem_object *obj);
+
+
+	/**
+	 * @gem_prime_get_sg_table:
+	 *
+	 * Deprecated hook in favour of &drm_gem_object_funcs.get_sg_table.
+	 */
+	struct sg_table *(*gem_prime_get_sg_table)(struct drm_gem_object *obj);
+
+	/**
+	 * @gem_prime_res_obj:
+	 *
+	 * Optional hook to look up the &reservation_object for an buffer when
+	 * exporting it.
+	 *
+	 * FIXME: This hook is deprecated. Users of this hook should be replaced
+	 * by setting &drm_gem_object.resv instead.
+	 */
 	struct reservation_object * (*gem_prime_res_obj)(
 				struct drm_gem_object *obj);
-	struct sg_table *(*gem_prime_get_sg_table)(struct drm_gem_object *obj);
+
+	/**
+	 * @gem_prime_import_sg_table:
+	 *
+	 * Optional hook used by the PRIME helper functions
+	 * drm_gem_prime_import() respectively drm_gem_prime_import_dev().
+	 */
 	struct drm_gem_object *(*gem_prime_import_sg_table)(
 				struct drm_device *dev,
 				struct dma_buf_attachment *attach,
 				struct sg_table *sgt);
+	/**
+	 * @gem_prime_vmap:
+	 *
+	 * Deprecated vmap hook for GEM drivers. Please use
+	 * &drm_gem_object_funcs.vmap instead.
+	 */
 	void *(*gem_prime_vmap)(struct drm_gem_object *obj);
+
+	/**
+	 * @gem_prime_vunmap:
+	 *
+	 * Deprecated vunmap hook for GEM drivers. Please use
+	 * &drm_gem_object_funcs.vunmap instead.
+	 */
 	void (*gem_prime_vunmap)(struct drm_gem_object *obj, void *vaddr);
+
+	/**
+	 * @gem_prime_mmap:
+	 *
+	 * mmap hook for GEM drivers, used to implement dma-buf mmap in the
+	 * PRIME helpers.
+	 *
+	 * FIXME: There's way too much duplication going on here, and also moved
+	 * to &drm_gem_object_funcs.
+	 */
 	int (*gem_prime_mmap)(struct drm_gem_object *obj,
 				struct vm_area_struct *vma);
 
@@ -662,6 +735,9 @@ struct drm_driver {
 
 	/**
 	 * @gem_vm_ops: Driver private ops for this object
+	 *
+	 * For GEM drivers this is deprecated in favour of
+	 * &drm_gem_object_funcs.vm_ops.
 	 */
 	const struct vm_operations_struct *gem_vm_ops;
 

include/drm/drm_gem.h

@@ -101,7 +101,7 @@ struct drm_gem_object_funcs {
 	/**
 	 * @pin:
 	 *
-	 * Pin backing buffer in memory.
+	 * Pin backing buffer in memory. Used by the drm_gem_map_attach() helper.
 	 *
 	 * This callback is optional.
 	 */
@@ -110,7 +110,7 @@ struct drm_gem_object_funcs {
 	/**
 	 * @unpin:
 	 *
-	 * Unpin backing buffer.
+	 * Unpin backing buffer. Used by the drm_gem_map_detach() helper.
 	 *
 	 * This callback is optional.
 	 */
@@ -120,16 +120,21 @@ struct drm_gem_object_funcs {
 	 * @get_sg_table:
 	 *
 	 * Returns a Scatter-Gather table representation of the buffer.
-	 * Used when exporting a buffer.
+	 * Used when exporting a buffer by the drm_gem_map_dma_buf() helper.
+	 * Releasing is done by calling dma_unmap_sg_attrs() and sg_free_table()
+	 * in drm_gem_unmap_buf(), therefore these helpers and this callback
+	 * here cannot be used for sg tables pointing at driver private memory
+	 * ranges.
 	 *
-	 * This callback is mandatory if buffer export is supported.
+	 * See also drm_prime_pages_to_sg().
 	 */
 	struct sg_table *(*get_sg_table)(struct drm_gem_object *obj);
 
 	/**
 	 * @vmap:
 	 *
-	 * Returns a virtual address for the buffer.
+	 * Returns a virtual address for the buffer. Used by the
+	 * drm_gem_dmabuf_vmap() helper.
 	 *
 	 * This callback is optional.
 	 */
@@ -138,7 +143,8 @@ struct drm_gem_object_funcs {
 	/**
 	 * @vunmap:
 	 *
-	 * Releases the the address previously returned by @vmap.
+	 * Releases the the address previously returned by @vmap. Used by the
+	 * drm_gem_dmabuf_vunmap() helper.
 	 *
 	 * This callback is optional.
 	 */