Re: [RFC PATCH v4 09/38] NTB: core: Add mw_set_trans_ranges() for subrange programming

On Sun, Jan 18, 2026 at 10:54:11PM +0900, Koichiro Den wrote:
> At the BAR level, multiple MWs may be packed into a single BAR. In
> addition, a single MW may itself be subdivided into multiple address
> subranges, each of which can be mapped independently by the underlying
> NTB hardware.
>
> Introduce an optional ntb_dev_ops callback, .mw_set_trans_ranges(), to
> describe and program such layouts explicitly. The helper allows an NTB
> driver to provide, for each MW, a list of contiguous subranges that
> together cover the MW address space.
>
> Signed-off-by: Koichiro Den <[email protected]>
> ---

Reviewed-by: Frank Li <[email protected]>
>  include/linux/ntb.h | 46 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
>
> diff --git a/include/linux/ntb.h b/include/linux/ntb.h
> index 8ff9d663096b..84908753f446 100644
> --- a/include/linux/ntb.h
> +++ b/include/linux/ntb.h
> @@ -206,6 +206,11 @@ static inline int ntb_ctx_ops_is_valid(const struct ntb_ctx_ops *ops)
>  		1;
>  }
>
> +struct ntb_mw_subrange {
> +	dma_addr_t	addr;
> +	resource_size_t	size;
> +};
> +
>  /**
>   * struct ntb_dev_ops - ntb device operations
>   * @port_number:	See ntb_port_number().
> @@ -218,6 +223,7 @@ static inline int ntb_ctx_ops_is_valid(const struct ntb_ctx_ops *ops)
>   * @mw_count:		See ntb_mw_count().
>   * @mw_get_align:	See ntb_mw_get_align().
>   * @mw_set_trans:	See ntb_mw_set_trans().
> + * @mw_set_trans_ranges:See ntb_mw_set_trans_ranges().
>   * @mw_clear_trans:	See ntb_mw_clear_trans().
>   * @peer_mw_count:	See ntb_peer_mw_count().
>   * @peer_mw_get_addr:	See ntb_peer_mw_get_addr().
> @@ -276,6 +282,9 @@ struct ntb_dev_ops {
>  			    resource_size_t *size_max);
>  	int (*mw_set_trans)(struct ntb_dev *ntb, int pidx, int widx,
>  			    dma_addr_t addr, resource_size_t size);
> +	int (*mw_set_trans_ranges)(struct ntb_dev *ntb, int pidx, int widx,
> +				   unsigned int num_ranges,
> +				   const struct ntb_mw_subrange *ranges);
>  	int (*mw_clear_trans)(struct ntb_dev *ntb, int pidx, int widx);
>  	int (*peer_mw_count)(struct ntb_dev *ntb);
>  	int (*peer_mw_get_addr)(struct ntb_dev *ntb, int widx,
> @@ -350,6 +359,7 @@ static inline int ntb_dev_ops_is_valid(const struct ntb_dev_ops *ops)
>  		ops->mw_get_align			&&
>  		(ops->mw_set_trans			||
>  		 ops->peer_mw_set_trans)		&&
> +		/* ops->mw_set_trans_ranges		&& */
>  		/* ops->mw_clear_trans			&& */
>  		ops->peer_mw_count			&&
>  		ops->peer_mw_get_addr			&&
> @@ -860,6 +870,42 @@ static inline int ntb_mw_set_trans(struct ntb_dev *ntb, int pidx, int widx,
>  	return ntb->ops->mw_set_trans(ntb, pidx, widx, addr, size);
>  }
>
> +/**
> + * ntb_mw_set_trans_ranges() - set the translations of an inbound memory
> + *                             window, composed of multiple subranges.
> + * @ntb:	NTB device context.
> + * @pidx:	Port index of peer device.
> + * @widx:	Memory window index.
> + * @num_ranges:	The number of ranges described by @ranges array.
> + * @ranges:	Array of subranges. The subranges are interpreted in ascending
> + *		window offset order (i.e. ranges[0] maps the first part of the MW,
> + *		ranges[1] the next part, ...).
> + *
> + * Return: Zero on success, otherwise an error number. If the driver does
> + *         not implement the callback, return -EOPNOTSUPP.
> + */
> +static inline int ntb_mw_set_trans_ranges(struct ntb_dev *ntb, int pidx, int widx,
> +					  unsigned int num_ranges,
> +					  const struct ntb_mw_subrange *ranges)
> +{
> +	if (!num_ranges || !ranges)
> +		return -EINVAL;
> +
> +	if (ntb->ops->mw_set_trans_ranges)
> +		return ntb->ops->mw_set_trans_ranges(ntb, pidx, widx,
> +						     num_ranges, ranges);
> +
> +	/*
> +	 * Fallback for drivers that only support the legacy single-range
> +	 * translation API.
> +	 */
> +	if (num_ranges == 1)
> +		return ntb_mw_set_trans(ntb, pidx, widx,
> +					ranges[0].addr, ranges[0].size);
> +
> +	return -EOPNOTSUPP;
> +}
> +
>  /**
>   * ntb_mw_clear_trans() - clear the translation address of an inbound memory
>   *                        window
> --
> 2.51.0
>