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dma-buf: doc polish for pin/unpin 

Motivated by a discussion with Christian and Thomas: Try to untangle a
bit what's relevant for importers and what's relevant for exporters.

Also add an assert that really only dynamic importers use the api
function, anything else doesn't make sense.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20201211155843.3348718-4-daniel.vetter@ffwll.ch
This commit is contained in:
Daniel Vetter 2020-12-11 16:58:43 +01:00
parent 8ccf0a29af
commit c545781e1c
2 changed files with 21 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
drivers/dma-buf/dma-buf.c
View File

@ -809,9 +809,15 @@ EXPORT_SYMBOL_GPL(dma_buf_detach);
/** /**
* dma_buf_pin - Lock down the DMA-buf * dma_buf_pin - Lock down the DMA-buf
*
* @attach: [in] attachment which should be pinned * @attach: [in] attachment which should be pinned
* *
* Only dynamic importers (who set up @attach with dma_buf_dynamic_attach()) may
* call this, and only for limited use cases like scanout and not for temporary
* pin operations. It is not permitted to allow userspace to pin arbitrary
* amounts of buffers through this interface.
*
* Buffers must be unpinned by calling dma_buf_unpin().
*
* Returns: * Returns:
* 0 on success, negative error code on failure. * 0 on success, negative error code on failure.
*/ */
@ -820,6 +826,8 @@ int dma_buf_pin(struct dma_buf_attachment *attach)
struct dma_buf *dmabuf = attach->dmabuf; struct dma_buf *dmabuf = attach->dmabuf;
int ret = 0; int ret = 0;
WARN_ON(!dma_buf_attachment_is_dynamic(attach));
dma_resv_assert_held(dmabuf->resv); dma_resv_assert_held(dmabuf->resv);
if (dmabuf->ops->pin) if (dmabuf->ops->pin)
@ -830,14 +838,19 @@ int dma_buf_pin(struct dma_buf_attachment *attach)
EXPORT_SYMBOL_GPL(dma_buf_pin); EXPORT_SYMBOL_GPL(dma_buf_pin);
/** /**
* dma_buf_unpin - Remove lock from DMA-buf * dma_buf_unpin - Unpin a DMA-buf
*
* @attach: [in] attachment which should be unpinned * @attach: [in] attachment which should be unpinned
*
* This unpins a buffer pinned by dma_buf_pin() and allows the exporter to move
* any mapping of @attach again and inform the importer through
* &dma_buf_attach_ops.move_notify.
*/ */
void dma_buf_unpin(struct dma_buf_attachment *attach) void dma_buf_unpin(struct dma_buf_attachment *attach)
{ {
struct dma_buf *dmabuf = attach->dmabuf; struct dma_buf *dmabuf = attach->dmabuf;
WARN_ON(!dma_buf_attachment_is_dynamic(attach));
dma_resv_assert_held(dmabuf->resv); dma_resv_assert_held(dmabuf->resv);
if (dmabuf->ops->unpin) if (dmabuf->ops->unpin)

8
include/linux/dma-buf.h
View File

@ -86,13 +86,15 @@ struct dma_buf_ops {
* @pin: * @pin:
* *
* This is called by dma_buf_pin() and lets the exporter know that the * This is called by dma_buf_pin() and lets the exporter know that the
* DMA-buf can't be moved any more. * DMA-buf can't be moved any more. The exporter should pin the buffer
* into system memory to make sure it is generally accessible by other
* devices.
* *
* This is called with the &dmabuf.resv object locked and is mutual * This is called with the &dmabuf.resv object locked and is mutual
* exclusive with @cache_sgt_mapping. * exclusive with @cache_sgt_mapping.
* *
* This callback is optional and should only be used in limited use * This is called automatically for non-dynamic importers from
* cases like scanout and not for temporary pin operations. * dma_buf_attach().
* *
* Returns: * Returns:
* *