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-rw-r--r--include/linux/dma-buf.h224
1 files changed, 193 insertions, 31 deletions
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 8daeb3ce0016..57828154e440 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -39,23 +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.
- * @end_cpu_access: [optional] called after cpu access to flush caches.
* @kmap_atomic: maps a page from the buffer into kernel address
* space, users may not block until the subsequent unmap call.
* This callback must not sleep.
@@ -63,43 +46,206 @@ struct dma_buf_attachment;
* This Callback must not sleep.
* @kmap: maps a page from the buffer into kernel address space.
* @kunmap: [optional] unmaps a page from the buffer.
- * @mmap: used to expose the backing storage to userspace. Note that the
- * mapping needs to be coherent - if the exporter doesn't directly
- * support this, it needs to fake coherency by shooting down any ptes
- * when transitioning away from the cpu domain.
* @vmap: [optional] creates a virtual mapping for the buffer into kernel
* address space. Same restrictions as for vmap and friends apply.
* @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 *);
+ /**
+ * @begin_cpu_access:
+ *
+ * This is called from dma_buf_begin_cpu_access() and allows the
+ * exporter to ensure that the memory is actually available for cpu
+ * access - the exporter might need to allocate or swap-in and pin the
+ * backing storage. The exporter also needs to ensure that cpu access is
+ * coherent for the access direction. The direction can be used by the
+ * exporter to optimize the cache flushing, i.e. access with a different
+ * direction (read instead of write) might return stale or even bogus
+ * data (e.g. when the exporter needs to copy the data to temporary
+ * storage).
+ *
+ * This callback is optional.
+ *
+ * FIXME: This is both called through the DMA_BUF_IOCTL_SYNC command
+ * from userspace (where storage shouldn't be pinned to avoid handing
+ * de-factor mlock rights to userspace) and for the kernel-internal
+ * users of the various kmap interfaces, where the backing storage must
+ * be pinned to guarantee that the atomic kmap calls can succeed. Since
+ * there's no in-kernel users of the kmap interfaces yet this isn't a
+ * real problem.
+ *
+ * Returns:
+ *
+ * 0 on success or a negative error code on failure. This can for
+ * example fail when the backing storage can't be allocated. Can also
+ * return -ERESTARTSYS or -EINTR when the call has been interrupted and
+ * needs to be restarted.
+ */
int (*begin_cpu_access)(struct dma_buf *, enum dma_data_direction);
+
+ /**
+ * @end_cpu_access:
+ *
+ * This is called from dma_buf_end_cpu_access() when the importer is
+ * done accessing the CPU. The exporter can use this to flush caches and
+ * unpin any resources pinned in @begin_cpu_access.
+ * The result of any dma_buf kmap calls after end_cpu_access is
+ * undefined.
+ *
+ * This callback is optional.
+ *
+ * Returns:
+ *
+ * 0 on success or a negative error code on failure. Can return
+ * -ERESTARTSYS or -EINTR when the call has been interrupted and needs
+ * to be restarted.
+ */
int (*end_cpu_access)(struct dma_buf *, enum dma_data_direction);
void *(*kmap_atomic)(struct dma_buf *, unsigned long);
void (*kunmap_atomic)(struct dma_buf *, unsigned long, void *);
void *(*kmap)(struct dma_buf *, unsigned long);
void (*kunmap)(struct dma_buf *, unsigned long, void *);
+ /**
+ * @mmap:
+ *
+ * This callback is used by the dma_buf_mmap() function
+ *
+ * Note that the mapping needs to be incoherent, userspace is expected
+ * to braket CPU access using the DMA_BUF_IOCTL_SYNC interface.
+ *
+ * Because dma-buf buffers have invariant size over their lifetime, the
+ * dma-buf core checks whether a vma is too large and rejects such
+ * mappings. The exporter hence does not need to duplicate this check.
+ * Drivers do not need to check this themselves.
+ *
+ * If an exporter needs to manually flush caches and hence needs to fake
+ * coherency for mmap support, it needs to be able to zap all the ptes
+ * pointing at the backing storage. Now linux mm needs a struct
+ * address_space associated with the struct file stored in vma->vm_file
+ * to do that with the function unmap_mapping_range. But the dma_buf
+ * framework only backs every dma_buf fd with the anon_file struct file,
+ * i.e. all dma_bufs share the same file.
+ *
+ * Hence exporters need to setup their own file (and address_space)
+ * association by setting vma->vm_file and adjusting vma->vm_pgoff in
+ * the dma_buf mmap callback. In the specific case of a gem driver the
+ * exporter could use the shmem file already provided by gem (and set
+ * vm_pgoff = 0). Exporters can then zap ptes by unmapping the
+ * corresponding range of the struct address_space associated with their
+ * own file.
+ *
+ * This callback is optional.
+ *
+ * Returns:
+ *
+ * 0 on success or a negative error code on failure.
+ */
int (*mmap)(struct dma_buf *, struct vm_area_struct *vma);
void *(*vmap)(struct dma_buf *);
@@ -124,6 +270,15 @@ 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 +315,11 @@ 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 +352,11 @@ 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, \