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dma-buf: Reorganize device dma access docs

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- Put the initial overview for dma-buf into dma-buf.rst.
- Put all the comments about detailed semantics into the right
  kernel-doc comment for functions or ops structure member.
- To allow that detail, switch the reworked kerneldoc to inline style
  for dma_buf_ops.
- Tie everything together into a much more streamlined overview
  comment, relying on the hyperlinks for all the details.
- Also sprinkle some links into the kerneldoc for dma_buf and
  dma_buf_attachment to tie it all together.

Cc: linux-doc@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20161209185309.1682-4-daniel.vetter@ffwll.ch
This commit is contained in:
Daniel Vetter
2016-12-09 19:53:07 +01:00
committed by Sumit Semwal
parent 24a367348a
commit 2904a8c131
5 changed files with 207 additions and 251 deletions
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133
include/linux/dma-buf.h
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@@ -39,19 +39,6 @@ struct dma_buf_attachment;
/**
* struct dma_buf_ops - operations possible on struct dma_buf
* @attach: [optional] allows different devices to 'attach' themselves to the
* given buffer. It might return -EBUSY to signal that backing storage
* is already allocated and incompatible with the requirements
* of requesting device.
* @detach: [optional] detach a given device from this buffer.
* @map_dma_buf: returns list of scatter pages allocated, increases usecount
* of the buffer. Requires atleast one attach to be called
* before. Returned sg list should already be mapped into
* _device_ address space. This call may sleep. May also return
* -EINTR. Should return -EINVAL if attach hasn't been called yet.
* @unmap_dma_buf: decreases usecount of buffer, might deallocate scatter
* pages.
* @release: release this buffer; to be called after the last dma_buf_put.
* @begin_cpu_access: [optional] called before cpu access to invalidate cpu
* caches and allocate backing storage (if not yet done)
* respectively pin the object into memory.
@@ -72,25 +59,109 @@ struct dma_buf_attachment;
* @vunmap: [optional] unmaps a vmap from the buffer
*/
struct dma_buf_ops {
/**
* @attach:
*
* This is called from dma_buf_attach() to make sure that a given
* &device can access the provided &dma_buf. Exporters which support
* buffer objects in special locations like VRAM or device-specific
* carveout areas should check whether the buffer could be move to
* system memory (or directly accessed by the provided device), and
* otherwise need to fail the attach operation.
*
* The exporter should also in general check whether the current
* allocation fullfills the DMA constraints of the new device. If this
* is not the case, and the allocation cannot be moved, it should also
* fail the attach operation.
*
* Any exporter-private housekeeping data can be stored in the priv
* pointer of &dma_buf_attachment structure.
*
* This callback is optional.
*
* Returns:
*
* 0 on success, negative error code on failure. It might return -EBUSY
* to signal that backing storage is already allocated and incompatible
* with the requirements of requesting device.
*/
int (*attach)(struct dma_buf *, struct device *,
struct dma_buf_attachment *);
struct dma_buf_attachment *);
/**
* @detach:
*
* This is called by dma_buf_detach() to release a &dma_buf_attachment.
* Provided so that exporters can clean up any housekeeping for an
* &dma_buf_attachment.
*
* This callback is optional.
*/
void (*detach)(struct dma_buf *, struct dma_buf_attachment *);
/* For {map,unmap}_dma_buf below, any specific buffer attributes
* required should get added to device_dma_parameters accessible
* via dev->dma_params.
/**
* @map_dma_buf:
*
* This is called by dma_buf_map_attachment() and is used to map a
* shared &dma_buf into device address space, and it is mandatory. It
* can only be called if @attach has been called successfully. This
* essentially pins the DMA buffer into place, and it cannot be moved
* any more
*
* This call may sleep, e.g. when the backing storage first needs to be
* allocated, or moved to a location suitable for all currently attached
* devices.
*
* Note that any specific buffer attributes required for this function
* should get added to device_dma_parameters accessible via
* device->dma_params from the &dma_buf_attachment. The @attach callback
* should also check these constraints.
*
* If this is being called for the first time, the exporter can now
* choose to scan through the list of attachments for this buffer,
* collate the requirements of the attached devices, and choose an
* appropriate backing storage for the buffer.
*
* Based on enum dma_data_direction, it might be possible to have
* multiple users accessing at the same time (for reading, maybe), or
* any other kind of sharing that the exporter might wish to make
* available to buffer-users.
*
* Returns:
*
* A &sg_table scatter list of or the backing storage of the DMA buffer,
* already mapped into the device address space of the &device attached
* with the provided &dma_buf_attachment.
*
* On failure, returns a negative error value wrapped into a pointer.
* May also return -EINTR when a signal was received while being
* blocked.
*/
struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *,
enum dma_data_direction);
enum dma_data_direction);
/**
* @unmap_dma_buf:
*
* This is called by dma_buf_unmap_attachment() and should unmap and
* release the &sg_table allocated in @map_dma_buf, and it is mandatory.
* It should also unpin the backing storage if this is the last mapping
* of the DMA buffer, it the exporter supports backing storage
* migration.
*/
void (*unmap_dma_buf)(struct dma_buf_attachment *,
struct sg_table *,
enum dma_data_direction);
struct sg_table *,
enum dma_data_direction);
/* TODO: Add try_map_dma_buf version, to return immed with -EBUSY
* if the call would block.
*/
/* after final dma_buf_put() */
/**
* @release:
*
* Called after the last dma_buf_put to release the &dma_buf, and
* mandatory.
*/
void (*release)(struct dma_buf *);
int (*begin_cpu_access)(struct dma_buf *, enum dma_data_direction);
@@ -124,6 +195,15 @@ struct dma_buf_ops {
* @poll: for userspace poll support
* @cb_excl: for userspace poll support
* @cb_shared: for userspace poll support
*
* This represents a shared buffer, created by calling dma_buf_export(). The
* userspace representation is a normal file descriptor, which can be created by
* calling dma_buf_fd().
*
* Shared dma buffers are reference counted using dma_buf_put() and
* get_dma_buf().
*
* Device DMA access is handled by the separate struct &dma_buf_attachment.
*/
struct dma_buf {
size_t size;
@@ -160,6 +240,11 @@ struct dma_buf {
* This structure holds the attachment information between the dma_buf buffer
* and its user device(s). The list contains one attachment struct per device
* attached to the buffer.
*
* An attachment is created by calling dma_buf_attach(), and released again by
* calling dma_buf_detach(). The DMA mapping itself needed to initiate a
* transfer is created by dma_buf_map_attachment() and freed again by calling
* dma_buf_unmap_attachment().
*/
struct dma_buf_attachment {
struct dma_buf *dmabuf;
@@ -192,9 +277,11 @@ struct dma_buf_export_info {
};
/**
* helper macro for exporters; zeros and fills in most common values
*
* DEFINE_DMA_BUF_EXPORT_INFO - helper macro for exporters
* @name: export-info name
*
* DEFINE_DMA_BUF_EXPORT_INFO macro defines the struct &dma_buf_export_info,
* zeroes it out and pre-populates exp_name in it.
*/
#define DEFINE_DMA_BUF_EXPORT_INFO(name) \
struct dma_buf_export_info name = { .exp_name = KBUILD_MODNAME, \