Hi Sumit,
On 12/26/2011 10:23 AM, Sumit Semwal wrote:
This is the first step in defining a dma buffer sharing mechanism.
A new buffer object dma_buf is added, with operations and API to allow easy
sharing of this buffer object across devices.
The framework allows:
- creation of a buffer object, its association with a file pointer, and
associated allocator-defined operations on that buffer. This operation is
called the 'export' operation.
- different devices to 'attach' themselves to this exported buffer object, to
facilitate backing storage negotiation, using dma_buf_attach() API.
- the exported buffer object to be shared with the other entity by asking for
its 'file-descriptor (fd)', and sharing the fd across.
- a received fd to get the buffer object back, where it can be accessed using
the associated exporter-defined operations.
- the exporter and user to share the scatterlist associated with this buffer
object using map_dma_buf and unmap_dma_buf operations.
[snip]
+/**
+ * struct dma_buf_attachment - holds device-buffer attachment data
+ * @dmabuf: buffer for this attachment.
+ * @dev: device attached to the buffer.
+ * @node: list of dma_buf_attachment.
+ * @priv: exporter specific attachment data.
+ *
+ * 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.
+ */
+struct dma_buf_attachment {
+ struct dma_buf *dmabuf;
+ struct device *dev;
+ struct list_head node;
+ void *priv;
+};
+
+#ifdef CONFIG_DMA_SHARED_BUFFER
+struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
+ struct device *dev);
+void dma_buf_detach(struct dma_buf *dmabuf,
+ struct dma_buf_attachment *dmabuf_attach);
+struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
+ size_t size, int flags);
+int dma_buf_fd(struct dma_buf *dmabuf);
+struct dma_buf *dma_buf_get(int fd);
+void dma_buf_put(struct dma_buf *dmabuf);
+
+struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
+ enum dma_data_direction);
+void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *);
I think that you should add enum dma_data_direction as an argument
unmap function. It was mentioned that the dma_buf_attachment should keep
cached and mapped sg_table for performance reasons. The field
dma_buf_attachment::priv seams to be a natural place to keep this sg_table.
To map a buffer the exporter calls dma_map_sg. It needs dma direction
as an argument. The problem is that dma_unmap_sg also needs this
argument but dma direction is not available neither in
dma_buf_unmap_attachment nor in unmap callback. Therefore the exporter
is forced to embed returned sg_table into a bigger structure where dma
direction is remembered. Refer to function vb2_dc_dmabuf_ops_map at
link below as an example:
http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/43793/focus=43797
Regards,
Tomasz Stanislawski
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