[RFC PATCH v4 11/38] NTB: core: Add .get_dma_dev() to ntb_dev_ops

Koichiro Den
2026-01-18T13:55:16Z

Not all NTB implementations are able to naturally do DMA mapping through
the NTB PCI device itself (e.g. due to IOMMU topology or non-PCI backing
devices).

Add an optional .get_dma_dev() callback and helper so clients can use
the appropriate struct device for DMA API allocations and mappings.

Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
include/linux/ntb.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)

diff --git a/include/linux/ntb.h b/include/linux/ntb.h
index aa888219732a..7ac8cb13e90d 100644
--- a/include/linux/ntb.h
+++ b/include/linux/ntb.h
@@ -262,6 +262,7 @@ struct ntb_mw_subrange {
* @msg_clear_mask: See ntb_msg_clear_mask().
* @msg_read: See ntb_msg_read().
* @peer_msg_write: See ntb_peer_msg_write().
+ * @get_dma_dev: See ntb_get_dma_dev().
* @get_private_data: See ntb_get_private_data().
*/
struct ntb_dev_ops {
@@ -339,6 +340,7 @@ struct ntb_dev_ops {
int (*msg_clear_mask)(struct ntb_dev *ntb, u64 mask_bits);
u32 (*msg_read)(struct ntb_dev *ntb, int *pidx, int midx);
int (*peer_msg_write)(struct ntb_dev *ntb, int pidx, int midx, u32 msg);
+ struct device *(*get_dma_dev)(struct ntb_dev *ntb);
void *(*get_private_data)(struct ntb_dev *ntb);
};

@@ -405,6 +407,7 @@ static inline int ntb_dev_ops_is_valid(const struct ntb_dev_ops *ops)
!ops->peer_msg_write == !ops->msg_count &&

/* Miscellaneous optional callbacks */
+ /* ops->get_dma_dev && */
/* ops->get_private_data && */
1;
}
@@ -1614,6 +1617,21 @@ static inline int ntb_peer_msg_write(struct ntb_dev *ntb, int pidx, int midx,
return ntb->ops->peer_msg_write(ntb, pidx, midx, msg);
}

+/**
+ * ntb_get_dma_dev() - get the device suitable for DMA mapping
+ * @ntb: NTB device context.
+ *
+ * Retrieve a struct device which is suitable for DMA mapping.
+ *
+ * Return: Pointer to struct device.
+ */
+static inline struct device __maybe_unused *ntb_get_dma_dev(struct ntb_dev *ntb)
+{
+ if (!ntb->ops->get_dma_dev)
+ return ntb->dev.parent;
+ return ntb->ops->get_dma_dev(ntb);
+}
+
/**
* ntb_get_private_data() - get private data specific to the hardware driver
* @ntb: NTB device context.
--
2.51.0