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authorDaniel Vetter <daniel.vetter@ffwll.ch>2020-12-11 16:58:43 +0100
committerDaniel Vetter <daniel.vetter@ffwll.ch>2020-12-16 11:28:34 +0100
commitc545781e1c55ab680dcc49c37212d5327b9d6812 (patch)
tree14152db8d82354f45b4ff3e89270bc4b4010734e
parentdma-buf: begin/end_cpu might lock the dma_resv lock (diff)
downloadlinux-c545781e1c55ab680dcc49c37212d5327b9d6812.tar.xz
linux-c545781e1c55ab680dcc49c37212d5327b9d6812.zip
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
-rw-r--r--drivers/dma-buf/dma-buf.c19
-rw-r--r--include/linux/dma-buf.h8
2 files changed, 21 insertions, 6 deletions
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index a0a02ef888da..b8465243eca2 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -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)
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 43802a31b25d..628681bf6c99 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -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:
*