Commit c545781e authored by Daniel Vetter's avatar Daniel Vetter
Browse files

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: default avatarChristian König <christian.koenig@amd.com>
Signed-off-by: default avatarDaniel 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
parent 8ccf0a29

drivers/dma-buf/dma-buf.c

+16 −3
Original line number Diff line number Diff line
@@ -809,9 +809,15 @@ EXPORT_SYMBOL_GPL(dma_buf_detach); 


/**

 * dma_buf_pin - Lock down the DMA-buf

 *

 * @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:

 * 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;

	int ret = 0;



	WARN_ON(!dma_buf_attachment_is_dynamic(attach));



	dma_resv_assert_held(dmabuf->resv);



	if (dmabuf->ops->pin)
@@ -830,14 +838,19 @@ int dma_buf_pin(struct dma_buf_attachment *attach) 
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

 *

 * 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)

{

	struct dma_buf *dmabuf = attach->dmabuf;



	WARN_ON(!dma_buf_attachment_is_dynamic(attach));



	dma_resv_assert_held(dmabuf->resv);



	if (dmabuf->ops->unpin)

include/linux/dma-buf.h

+5 −3
Original line number Diff line number Diff line
@@ -86,13 +86,15 @@ struct dma_buf_ops { 
	 * @pin:

	 *

	 * 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

	 * exclusive with @cache_sgt_mapping.

	 *

	 * This callback is optional and should only be used in limited use

	 * cases like scanout and not for temporary pin operations.

	 * This is called automatically for non-dynamic importers from

	 * dma_buf_attach().

	 *

	 * Returns:

	 *