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

Frank Li
2026-01-19T20:09:30Z

On Sun, Jan 18, 2026 at 10:54:13PM +0900, Koichiro Den wrote:
> 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)

I remember if there are inline, needn't __maybe_unused.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
> +{
> + 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
>