[PATCH v5 1/6] dma-buf: Add dma_buf_{begin,end}_access()

Paul Cercueil
2024-01-19T14:14:21Z

These functions should be used by device drivers when they start and
stop accessing the data of DMABUF. It allows DMABUF importers to cache
the dma_buf_attachment while ensuring that the data they want to access
is available for their device when the DMA transfers take place.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

---
v5: New patch
---
drivers/dma-buf/dma-buf.c | 66 +++++++++++++++++++++++++++++++++++++++
include/linux/dma-buf.h | 37 ++++++++++++++++++++++
2 files changed, 103 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 8fe5aa67b167..a8bab6c18fcd 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -830,6 +830,8 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
* - dma_buf_mmap()
* - dma_buf_begin_cpu_access()
* - dma_buf_end_cpu_access()
+ * - dma_buf_begin_access()
+ * - dma_buf_end_access()
* - dma_buf_map_attachment_unlocked()
* - dma_buf_unmap_attachment_unlocked()
* - dma_buf_vmap_unlocked()
@@ -1602,6 +1604,70 @@ void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map)
}
EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap_unlocked, DMA_BUF);

+/**
+ * @dma_buf_begin_access - Call before any hardware access from/to the DMABUF
+ * @attach: [in] attachment used for hardware access
+ * @sg_table: [in] scatterlist used for the DMA transfer
+ * @direction: [in] direction of DMA transfer
+ */
+int dma_buf_begin_access(struct dma_buf_attachment *attach,
+ struct sg_table *sgt, enum dma_data_direction dir)
+{
+ struct dma_buf *dmabuf;
+ bool cookie;
+ int ret;
+
+ if (WARN_ON(!attach))
+ return -EINVAL;
+
+ dmabuf = attach->dmabuf;
+
+ if (!dmabuf->ops->begin_access)
+ return 0;
+
+ cookie = dma_fence_begin_signalling();
+ ret = dmabuf->ops->begin_access(attach, sgt, dir);
+ dma_fence_end_signalling(cookie);
+
+ if (WARN_ON_ONCE(ret))
+ return ret;
+
+ return 0;
+}
+EXPORT_SYMBOL_NS_GPL(dma_buf_begin_access, DMA_BUF);
+
+/**
+ * @dma_buf_end_access - Call after any hardware access from/to the DMABUF
+ * @attach: [in] attachment used for hardware access
+ * @sg_table: [in] scatterlist used for the DMA transfer
+ * @direction: [in] direction of DMA transfer
+ */
+int dma_buf_end_access(struct dma_buf_attachment *attach,
+ struct sg_table *sgt, enum dma_data_direction dir)
+{
+ struct dma_buf *dmabuf;
+ bool cookie;
+ int ret;
+
+ if (WARN_ON(!attach))
+ return -EINVAL;
+
+ dmabuf = attach->dmabuf;
+
+ if (!dmabuf->ops->end_access)
+ return 0;
+
+ cookie = dma_fence_begin_signalling();
+ ret = dmabuf->ops->end_access(attach, sgt, dir);
+ dma_fence_end_signalling(cookie);
+
+ if (WARN_ON_ONCE(ret))
+ return ret;
+
+ return 0;
+}
+EXPORT_SYMBOL_NS_GPL(dma_buf_end_access, DMA_BUF);
+
#ifdef CONFIG_DEBUG_FS
static int dma_buf_debug_show(struct seq_file *s, void *unused)
{
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 8ff4add71f88..8ba612c7cc16 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -246,6 +246,38 @@ struct dma_buf_ops {
*/
int (*end_cpu_access)(struct dma_buf *, enum dma_data_direction);

+ /**
+ * @begin_access:
+ *
+ * This is called from dma_buf_begin_access() when a device driver
+ * wants to access the data of the DMABUF. The exporter can use this
+ * to flush/sync the caches if needed.
+ *
+ * This callback is optional.
+ *
+ * Returns:
+ *
+ * 0 on success or a negative error code on failure.
+ */
+ int (*begin_access)(struct dma_buf_attachment *, struct sg_table *,
+ enum dma_data_direction);
+
+ /**
+ * @end_access:
+ *
+ * This is called from dma_buf_end_access() when a device driver is
+ * done accessing the data of the DMABUF. The exporter can use this
+ * to flush/sync the caches if needed.
+ *
+ * This callback is optional.
+ *
+ * Returns:
+ *
+ * 0 on success or a negative error code on failure.
+ */
+ int (*end_access)(struct dma_buf_attachment *, struct sg_table *,
+ enum dma_data_direction);
+
/**
* @mmap:
*
@@ -606,6 +638,11 @@ void dma_buf_detach(struct dma_buf *dmabuf,
int dma_buf_pin(struct dma_buf_attachment *attach);
void dma_buf_unpin(struct dma_buf_attachment *attach);

+int dma_buf_begin_access(struct dma_buf_attachment *attach,
+ struct sg_table *sgt, enum dma_data_direction dir);
+int dma_buf_end_access(struct dma_buf_attachment *attach,
+ struct sg_table *sgt, enum dma_data_direction dir);
+
struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info);

int dma_buf_fd(struct dma_buf *dmabuf, int flags);
--
2.43.0