[PATCH v2 3/5] dma-buf: Move all dma-bufs to dynamic locking specification

From: Dmitry Osipenko
Date: Mon Jul 25 2022 - 11:22:11 EST

This patch moves the non-dynamic dma-buf users over to the dynamic
locking specification. The strict locking convention prevents deadlock
situation for dma-buf importers and exporters.

Previously the "unlocked" versions of the dma-buf API functions weren't
taking the reservation lock and this patch makes them to take the lock.

Intel and AMD GPU drivers already were mapping imported dma-bufs under
the held lock, hence the "locked" variant of the functions are added
for them and the drivers are updated to use the "locked" versions.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
---
Documentation/driver-api/dma-buf.rst | 6 +
drivers/dma-buf/dma-buf.c | 186 ++++++++++++++++-----
drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 4 +-
drivers/gpu/drm/drm_prime.c | 4 +-
drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 8 +-
include/linux/dma-buf.h | 28 ++--
6 files changed, 179 insertions(+), 57 deletions(-)

diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst
index 36a76cbe9095..622b8156d212 100644
--- a/Documentation/driver-api/dma-buf.rst
+++ b/Documentation/driver-api/dma-buf.rst
@@ -119,6 +119,12 @@ DMA Buffer ioctls

.. kernel-doc:: include/uapi/linux/dma-buf.h

+DMA-BUF locking convention
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/dma-buf.c
+ :doc: locking convention
+
Kernel Functions and Structures Reference
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index d16237a6ffaa..bfdd551c7571 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -559,7 +559,7 @@ static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
* 2. Userspace passes this file-descriptors to all drivers it wants this buffer
* to share with: First the file descriptor is converted to a &dma_buf using
* dma_buf_get(). Then the buffer is attached to the device using
- * dma_buf_attach().
+ * dma_buf_attach_unlocked().
*
* Up to this stage the exporter is still free to migrate or reallocate the
* backing storage.
@@ -569,8 +569,8 @@ static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
* dma_buf_map_attachment() and dma_buf_unmap_attachment().
*
* 4. Once a driver is done with a shared buffer it needs to call
- * dma_buf_detach() (after cleaning up any mappings) and then release the
- * reference acquired with dma_buf_get() by calling dma_buf_put().
+ * dma_buf_detach_unlocked() (after cleaning up any mappings) and then
+ * release the reference acquired with dma_buf_get() by calling dma_buf_put().
*
* For the detailed semantics exporters are expected to implement see
* &dma_buf_ops.
@@ -794,6 +794,63 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
return sg_table;
}

+/**
+ * DOC: locking convention
+ *
+ * In order to avoid deadlock situations between dma-buf exports and importers,
+ * all dma-buf API users must follow the common dma-buf locking convention.
+ *
+ * Convention for importers
+ *
+ * 1. Importers must hold the dma-buf reservation lock when calling these
+ * functions:
+ *
+ * - dma_buf_pin()
+ * - dma_buf_unpin()
+ * - dma_buf_move_notify()
+ * - dma_buf_map_attachment_locked()
+ * - dma_buf_unmap_attachment_locked()
+ *
+ * 2. Importers must not hold the dma-buf reservation lock when calling these
+ * functions:
+ *
+ * - dma_buf_attach_unlocked()
+ * - dma_buf_dynamic_attach_unlocked()
+ * - dma_buf_detach_unlocked()
+ * - dma_buf_export(
+ * - dma_buf_fd()
+ * - dma_buf_get()
+ * - dma_buf_put()
+ * - dma_buf_begin_cpu_access()
+ * - dma_buf_end_cpu_access()
+ * - dma_buf_map_attachment_unlocked()
+ * - dma_buf_unmap_attachment_unlocked()
+ * - dma_buf_vmap_unlocked()
+ * - dma_buf_vunmap_unlocked()
+ *
+ * Convention for exporters
+ *
+ * 1. These &dma_buf_ops callbacks are invoked with unlocked dma-buf
+ * reservation and exporter can take the lock:
+ *
+ * - &dma_buf_ops.attach()
+ * - &dma_buf_ops.detach()
+ * - &dma_buf_ops.release()
+ * - &dma_buf_ops.begin_cpu_access()
+ * - &dma_buf_ops.end_cpu_access()
+ *
+ * 2. These &dma_buf_ops callbacks are invoked with locked dma-buf
+ * reservation and exporter can't take the lock:
+ *
+ * - &dma_buf_ops.pin()
+ * - &dma_buf_ops.unpin()
+ * - &dma_buf_ops.map_dma_buf()
+ * - &dma_buf_ops.unmap_dma_buf()
+ * - &dma_buf_ops.mmap()
+ * - &dma_buf_ops.vmap()
+ * - &dma_buf_ops.vunmap()
+ */
+
/**
* dma_buf_dynamic_attach_unlocked - Add the device to dma_buf's attachments list
* @dmabuf: [in] buffer to attach device to.
@@ -802,7 +859,7 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
* @importer_priv: [in] importer private pointer for the attachment
*
* Returns struct dma_buf_attachment pointer for this attachment. Attachments
- * must be cleaned up by calling dma_buf_detach().
+ * must be cleaned up by calling dma_buf_detach_unlocked().
*
* Optionally this calls &dma_buf_ops.attach to allow device-specific attach
* functionality.
@@ -858,8 +915,8 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev,
dma_buf_is_dynamic(dmabuf)) {
struct sg_table *sgt;

+ dma_resv_lock(attach->dmabuf->resv, NULL);
if (dma_buf_is_dynamic(attach->dmabuf)) {
- dma_resv_lock(attach->dmabuf->resv, NULL);
ret = dmabuf->ops->pin(attach);
if (ret)
goto err_unlock;
@@ -872,8 +929,7 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev,
ret = PTR_ERR(sgt);
goto err_unpin;
}
- if (dma_buf_is_dynamic(attach->dmabuf))
- dma_resv_unlock(attach->dmabuf->resv);
+ dma_resv_unlock(attach->dmabuf->resv);
attach->sgt = sgt;
attach->dir = DMA_BIDIRECTIONAL;
}
@@ -889,8 +945,7 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev,
dmabuf->ops->unpin(attach);

err_unlock:
- if (dma_buf_is_dynamic(attach->dmabuf))
- dma_resv_unlock(attach->dmabuf->resv);
+ dma_resv_unlock(attach->dmabuf->resv);

dma_buf_detach_unlocked(dmabuf, attach);
return ERR_PTR(ret);
@@ -927,7 +982,7 @@ static void __unmap_dma_buf(struct dma_buf_attachment *attach,
* @dmabuf: [in] buffer to detach from.
* @attach: [in] attachment to be detached; is free'd after this call.
*
- * Clean up a device attachment obtained by calling dma_buf_attach().
+ * Clean up a device attachment obtained by calling dma_buf_attach_unlocked().
*
* Optionally this calls &dma_buf_ops.detach for device-specific detach.
*/
@@ -937,21 +992,19 @@ void dma_buf_detach_unlocked(struct dma_buf *dmabuf,
if (WARN_ON(!dmabuf || !attach))
return;

+ dma_resv_lock(attach->dmabuf->resv, NULL);
+
if (attach->sgt) {
- if (dma_buf_is_dynamic(attach->dmabuf))
- dma_resv_lock(attach->dmabuf->resv, NULL);

__unmap_dma_buf(attach, attach->sgt, attach->dir);

- if (dma_buf_is_dynamic(attach->dmabuf)) {
+ if (dma_buf_is_dynamic(attach->dmabuf))
dmabuf->ops->unpin(attach);
- dma_resv_unlock(attach->dmabuf->resv);
- }
}
-
- dma_resv_lock(dmabuf->resv, NULL);
list_del(&attach->node);
+
dma_resv_unlock(dmabuf->resv);
+
if (dmabuf->ops->detach)
dmabuf->ops->detach(dmabuf, attach);

@@ -1030,10 +1083,11 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_unpin, DMA_BUF);
*
* Important: Dynamic importers must wait for the exclusive fence of the struct
* dma_resv attached to the DMA-BUF first.
+ *
+ * Importer is responsible for holding dmabuf's reservation lock.
*/
-struct sg_table *
-dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
- enum dma_data_direction direction)
+struct sg_table *dma_buf_map_attachment_locked(struct dma_buf_attachment *attach,
+ enum dma_data_direction direction)
{
struct sg_table *sg_table;
int r;
@@ -1043,8 +1097,7 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
if (WARN_ON(!attach || !attach->dmabuf))
return ERR_PTR(-EINVAL);

- if (dma_buf_attachment_is_dynamic(attach))
- dma_resv_assert_held(attach->dmabuf->resv);
+ dma_resv_assert_held(attach->dmabuf->resv);

if (attach->sgt) {
/*
@@ -1059,7 +1112,6 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
}

if (dma_buf_is_dynamic(attach->dmabuf)) {
- dma_resv_assert_held(attach->dmabuf->resv);
if (!IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) {
r = attach->dmabuf->ops->pin(attach);
if (r)
@@ -1099,10 +1151,38 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
#endif /* CONFIG_DMA_API_DEBUG */
return sg_table;
}
+EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment_locked, DMA_BUF);
+
+/**
+ * dma_buf_map_attachment_unlocked - Returns the scatterlist table of the attachment;
+ * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
+ * dma_buf_ops.
+ * @attach: [in] attachment whose scatterlist is to be returned
+ * @direction: [in] direction of DMA transfer
+ *
+ * Unlocked variant of dma_buf_map_attachment_locked().
+ */
+struct sg_table *
+dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach,
+ enum dma_data_direction direction)
+{
+ struct sg_table *sg_table;
+
+ might_sleep();
+
+ if (WARN_ON(!attach || !attach->dmabuf))
+ return ERR_PTR(-EINVAL);
+
+ dma_resv_lock(attach->dmabuf->resv, NULL);
+ sg_table = dma_buf_map_attachment_locked(attach, direction);
+ dma_resv_unlock(attach->dmabuf->resv);
+
+ return sg_table;
+}
EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment_unlocked, DMA_BUF);

/**
- * dma_buf_unmap_attachment_unlocked - unmaps and decreases usecount of the buffer;might
+ * dma_buf_unmap_attachment_locked - unmaps and decreases usecount of the buffer;might
* deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
* dma_buf_ops.
* @attach: [in] attachment to unmap buffer from
@@ -1110,31 +1190,51 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment_unlocked, DMA_BUF);
* @direction: [in] direction of DMA transfer
*
* This unmaps a DMA mapping for @attached obtained by dma_buf_map_attachment().
+ *
+ * Importer is responsible for holding dmabuf's reservation lock.
*/
-void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach,
- struct sg_table *sg_table,
- enum dma_data_direction direction)
+void dma_buf_unmap_attachment_locked(struct dma_buf_attachment *attach,
+ struct sg_table *sg_table,
+ enum dma_data_direction direction)
{
might_sleep();

- if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
- return;
-
- if (dma_buf_attachment_is_dynamic(attach))
- dma_resv_assert_held(attach->dmabuf->resv);
+ dma_resv_assert_held(attach->dmabuf->resv);

if (attach->sgt == sg_table)
return;

- if (dma_buf_is_dynamic(attach->dmabuf))
- dma_resv_assert_held(attach->dmabuf->resv);
-
__unmap_dma_buf(attach, sg_table, direction);

if (dma_buf_is_dynamic(attach->dmabuf) &&
!IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
dma_buf_unpin(attach);
}
+EXPORT_SYMBOL_NS_GPL(dma_buf_unmap_attachment_locked, DMA_BUF);
+
+/**
+ * dma_buf_unmap_attachment_unlocked - unmaps and decreases usecount of the buffer;might
+ * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
+ * dma_buf_ops.
+ * @attach: [in] attachment to unmap buffer from
+ * @sg_table: [in] scatterlist info of the buffer to unmap
+ * @direction: [in] direction of DMA transfer
+ *
+ * Unlocked variant of dma_buf_unmap_attachment_locked().
+ */
+void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach,
+ struct sg_table *sg_table,
+ enum dma_data_direction direction)
+{
+ might_sleep();
+
+ if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
+ return;
+
+ dma_resv_lock(attach->dmabuf->resv, NULL);
+ dma_buf_unmap_attachment_locked(attach, sg_table, direction);
+ dma_resv_unlock(attach->dmabuf->resv);
+}
EXPORT_SYMBOL_NS_GPL(dma_buf_unmap_attachment_unlocked, DMA_BUF);

/**
@@ -1174,8 +1274,8 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_move_notify, DMA_BUF);
*
* Interfaces::
*
- * void \*dma_buf_vmap(struct dma_buf \*dmabuf, struct iosys_map \*map)
- * void dma_buf_vunmap(struct dma_buf \*dmabuf, struct iosys_map \*map)
+ * void \*dma_buf_vmap_unlocked(struct dma_buf \*dmabuf, struct iosys_map \*map)
+ * void dma_buf_vunmap_unlocked(struct dma_buf \*dmabuf, struct iosys_map \*map)
*
* The vmap call can fail if there is no vmap support in the exporter, or if
* it runs out of vmalloc space. Note that the dma-buf layer keeps a reference
@@ -1348,6 +1448,8 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_end_cpu_access, DMA_BUF);
int dma_buf_mmap_unlocked(struct dma_buf *dmabuf, struct vm_area_struct *vma,
unsigned long pgoff)
{
+ int ret;
+
if (WARN_ON(!dmabuf || !vma))
return -EINVAL;

@@ -1368,7 +1470,11 @@ int dma_buf_mmap_unlocked(struct dma_buf *dmabuf, struct vm_area_struct *vma,
vma_set_file(vma, dmabuf->file);
vma->vm_pgoff = pgoff;

- return dmabuf->ops->mmap(dmabuf, vma);
+ dma_resv_lock(dmabuf->resv, NULL);
+ ret = dmabuf->ops->mmap(dmabuf, vma);
+ dma_resv_unlock(dmabuf->resv);
+
+ return ret;
}
EXPORT_SYMBOL_NS_GPL(dma_buf_mmap_unlocked, DMA_BUF);

@@ -1401,6 +1507,7 @@ int dma_buf_vmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map)
if (!dmabuf->ops->vmap)
return -EINVAL;

+ dma_resv_lock(dmabuf->resv, NULL);
mutex_lock(&dmabuf->lock);
if (dmabuf->vmapping_counter) {
dmabuf->vmapping_counter++;
@@ -1422,6 +1529,7 @@ int dma_buf_vmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map)

out_unlock:
mutex_unlock(&dmabuf->lock);
+ dma_resv_unlock(dmabuf->resv);
return ret;
}
EXPORT_SYMBOL_NS_GPL(dma_buf_vmap_unlocked, DMA_BUF);
@@ -1440,6 +1548,7 @@ void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map)
BUG_ON(dmabuf->vmapping_counter == 0);
BUG_ON(!iosys_map_is_equal(&dmabuf->vmap_ptr, map));

+ dma_resv_lock(dmabuf->resv, NULL);
mutex_lock(&dmabuf->lock);
if (--dmabuf->vmapping_counter == 0) {
if (dmabuf->ops->vunmap)
@@ -1447,6 +1556,7 @@ void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map)
iosys_map_clear(&dmabuf->vmap_ptr);
}
mutex_unlock(&dmabuf->lock);
+ dma_resv_unlock(dmabuf->resv);
}
EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap_unlocked, DMA_BUF);

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index dd6ac1606316..1b426116c22e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -882,7 +882,7 @@ static int amdgpu_ttm_backend_bind(struct ttm_device *bdev,
struct sg_table *sgt;

attach = gtt->gobj->import_attach;
- sgt = dma_buf_map_attachment_unlocked(attach, DMA_BIDIRECTIONAL);
+ sgt = dma_buf_map_attachment_locked(attach, DMA_BIDIRECTIONAL);
if (IS_ERR(sgt))
return PTR_ERR(sgt);

@@ -1007,7 +1007,7 @@ static void amdgpu_ttm_backend_unbind(struct ttm_device *bdev,
struct dma_buf_attachment *attach;

attach = gtt->gobj->import_attach;
- dma_buf_unmap_attachment_unlocked(attach, ttm->sg, DMA_BIDIRECTIONAL);
+ dma_buf_unmap_attachment_locked(attach, ttm->sg, DMA_BIDIRECTIONAL);
ttm->sg = NULL;
}

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 1bd234fd21a5..b75ef1756873 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -678,7 +678,7 @@ int drm_gem_dmabuf_vmap(struct dma_buf *dma_buf, struct iosys_map *map)
{
struct drm_gem_object *obj = dma_buf->priv;

- return drm_gem_vmap_unlocked(obj, map);
+ return drm_gem_vmap(obj, map);
}
EXPORT_SYMBOL(drm_gem_dmabuf_vmap);

@@ -694,7 +694,7 @@ void drm_gem_dmabuf_vunmap(struct dma_buf *dma_buf, struct iosys_map *map)
{
struct drm_gem_object *obj = dma_buf->priv;

- drm_gem_vunmap_unlocked(obj, map);
+ drm_gem_vunmap(obj, map);
}
EXPORT_SYMBOL(drm_gem_dmabuf_vunmap);

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index cc54a5b1d6ae..d1bb6a3760e8 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -241,8 +241,8 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)

assert_object_held(obj);

- pages = dma_buf_map_attachment_unlocked(obj->base.import_attach,
- DMA_BIDIRECTIONAL);
+ pages = dma_buf_map_attachment_locked(obj->base.import_attach,
+ DMA_BIDIRECTIONAL);
if (IS_ERR(pages))
return PTR_ERR(pages);

@@ -270,8 +270,8 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)
static void i915_gem_object_put_pages_dmabuf(struct drm_i915_gem_object *obj,
struct sg_table *pages)
{
- dma_buf_unmap_attachment_unlocked(obj->base.import_attach, pages,
- DMA_BIDIRECTIONAL);
+ dma_buf_unmap_attachment_locked(obj->base.import_attach, pages,
+ DMA_BIDIRECTIONAL);
}

static const struct drm_i915_gem_object_ops i915_gem_object_dmabuf_ops = {
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 9ab09569dec1..e7a6a8d28862 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -46,7 +46,7 @@ struct dma_buf_ops {
/**
* @attach:
*
- * This is called from dma_buf_attach() to make sure that a given
+ * This is called from dma_buf_attach_unlocked() to make sure that a given
* &dma_buf_attachment.dev 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
@@ -74,7 +74,7 @@ struct dma_buf_ops {
/**
* @detach:
*
- * This is called by dma_buf_detach() to release a &dma_buf_attachment.
+ * This is called by dma_buf_detach_unlocked() to release a &dma_buf_attachment.
* Provided so that exporters can clean up any housekeeping for an
* &dma_buf_attachment.
*
@@ -94,7 +94,7 @@ struct dma_buf_ops {
* exclusive with @cache_sgt_mapping.
*
* This is called automatically for non-dynamic importers from
- * dma_buf_attach().
+ * dma_buf_attach_unlocked().
*
* Note that similar to non-dynamic exporters in their @map_dma_buf
* callback the driver must guarantee that the memory is available for
@@ -124,8 +124,8 @@ struct dma_buf_ops {
/**
* @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
+ * This is called by dma_buf_map_attachment_locked() 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 call may sleep, e.g. when the backing storage first needs to be
@@ -181,8 +181,8 @@ struct dma_buf_ops {
/**
* @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.
+ * This is called by dma_buf_unmap_attachment_locked() and should unmap
+ * and release the &sg_table allocated in @map_dma_buf, and it is mandatory.
* For static dma_buf handling this might also unpin the backing
* storage if this is the last mapping of the DMA buffer.
*/
@@ -509,10 +509,10 @@ struct dma_buf_attach_ops {
* 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().
+ * An attachment is created by calling dma_buf_attach_unlocked(), and released
+ * again by calling dma_buf_detach_unlocked(). The DMA mapping itself needed to
+ * initiate a transfer is created by dma_buf_map_attachment_locked() and freed
+ * again by calling dma_buf_unmap_attachment_locked().
*/
struct dma_buf_attachment {
struct dma_buf *dmabuf;
@@ -626,6 +626,12 @@ void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *,
struct sg_table *,
enum dma_data_direction);

+struct sg_table *dma_buf_map_attachment_locked(struct dma_buf_attachment *,
+ enum dma_data_direction);
+void dma_buf_unmap_attachment_locked(struct dma_buf_attachment *attach,
+ struct sg_table *sg_table,
+ enum dma_data_direction direction);
+
void dma_buf_move_notify(struct dma_buf *dma_buf);
int dma_buf_begin_cpu_access(struct dma_buf *dma_buf,
enum dma_data_direction dir);
--
2.36.1