Re: [RFC PATCH v4 16/38] NTB: ntb_transport: Move TX memory window setup into setup_qp_mw()

Frank Li
2026-01-19T20:37:02Z

On Sun, Jan 18, 2026 at 10:54:18PM +0900, Koichiro Den wrote:
> Historically both TX and RX have assumed the same per-QP MW slice
> (tx_max_entry == remote rx_max_entry), while those are calculated
> separately in different places (pre and post the link-up negotiation
> point). This has been safe because nt->link_is_up is never set to true
> unless the pre-determined qp_count are the same among them, and qp_count
> is typically limited to nt->mw_count, which should be carefully
> configured by admin.
>
> However, setup_qp_mw can actually split mw and handle multi-qps in one
> MW properly, so qp_count needs not to be limited by nt->mw_count. Once
> we relax the limitation, pre-determined qp_count can differ among host
> side and endpoint, and link-up negotiation can easily fail.
>
> Move the TX MW configuration (per-QP offset and size) into
> ntb_transport_setup_qp_mw() so that both RX and TX layout decisions are
> centralized in a single helper. ntb_transport_init_queue() now deals
> only with per-QP software state, not with MW layout.
>
> This keeps the previous behavior, while preparing for relaxing the
> qp_count limitation and improving readability.
>
> No functional change is intended.
>
> Signed-off-by: Koichiro Den <den@valinux.co.jp>
> ---
> drivers/ntb/ntb_transport.c | 76 ++++++++++++++++---------------------
> 1 file changed, 32 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
> index d5a544bf8fd6..57a21f2daac6 100644
> --- a/drivers/ntb/ntb_transport.c
> +++ b/drivers/ntb/ntb_transport.c
> @@ -569,7 +569,10 @@ static int ntb_transport_setup_qp_mw(struct ntb_transport_ctx *nt,
> struct ntb_transport_mw *mw;
> struct ntb_dev *ndev = nt->ndev;
> struct ntb_queue_entry *entry;
> - unsigned int rx_size, num_qps_mw;
> + phys_addr_t mw_base;
> + resource_size_t mw_size;
> + unsigned int rx_size, tx_size, num_qps_mw;
> + u64 qp_offset;
> unsigned int mw_num, mw_count, qp_count;
> unsigned int i;
> int node;
> @@ -588,13 +591,38 @@ static int ntb_transport_setup_qp_mw(struct ntb_transport_ctx *nt,
> else
> num_qps_mw = qp_count / mw_count;
>
> - rx_size = (unsigned int)mw->xlat_size / num_qps_mw;
> - qp->rx_buff = mw->virt_addr + rx_size * (qp_num / mw_count);
> - rx_size -= sizeof(struct ntb_rx_info);
> + mw_base = nt->mw_vec[mw_num].phys_addr;
> + mw_size = nt->mw_vec[mw_num].phys_size;
> +
> + if (mw_size > mw->xlat_size)
> + mw_size = mw->xlat_size;

old code have not check this.

Frank
> + if (max_mw_size && mw_size > max_mw_size)
> + mw_size = max_mw_size;
> +
> + tx_size = (unsigned int)mw_size / num_qps_mw;
> + qp_offset = tx_size * (qp_num / mw_count);
> +
> + qp->rx_buff = mw->virt_addr + qp_offset;
> +
> + qp->tx_mw_size = tx_size;
> + qp->tx_mw = nt->mw_vec[mw_num].vbase + qp_offset;
> + if (!qp->tx_mw)
> + return -EINVAL;
> +
> + qp->tx_mw_phys = mw_base + qp_offset;
> + if (!qp->tx_mw_phys)
> + return -EINVAL;
>
> + rx_size = tx_size;
> + rx_size -= sizeof(struct ntb_rx_info);
> qp->remote_rx_info = qp->rx_buff + rx_size;
>
> + tx_size -= sizeof(struct ntb_rx_info);
> + qp->rx_info = qp->tx_mw + tx_size;
> +
> /* Due to housekeeping, there must be atleast 2 buffs */
> + qp->tx_max_frame = min(transport_mtu, tx_size / 2);
> + qp->tx_max_entry = tx_size / qp->tx_max_frame;
> qp->rx_max_frame = min(transport_mtu, rx_size / 2);
> qp->rx_max_entry = rx_size / qp->rx_max_frame;
> qp->rx_index = 0;
> @@ -1132,16 +1160,6 @@ static int ntb_transport_init_queue(struct ntb_transport_ctx *nt,
> unsigned int qp_num)
> {
> struct ntb_transport_qp *qp;
> - phys_addr_t mw_base;
> - resource_size_t mw_size;
> - unsigned int num_qps_mw, tx_size;
> - unsigned int mw_num, mw_count, qp_count;
> - u64 qp_offset;
> -
> - mw_count = nt->mw_count;
> - qp_count = nt->qp_count;
> -
> - mw_num = QP_TO_MW(nt, qp_num);
>
> qp = &nt->qp_vec[qp_num];
> qp->qp_num = qp_num;
> @@ -1151,36 +1169,6 @@ static int ntb_transport_init_queue(struct ntb_transport_ctx *nt,
> qp->event_handler = NULL;
> ntb_qp_link_context_reset(qp);
>
> - if (mw_num < qp_count % mw_count)
> - num_qps_mw = qp_count / mw_count + 1;
> - else
> - num_qps_mw = qp_count / mw_count;
> -
> - mw_base = nt->mw_vec[mw_num].phys_addr;
> - mw_size = nt->mw_vec[mw_num].phys_size;
> -
> - if (max_mw_size && mw_size > max_mw_size)
> - mw_size = max_mw_size;
> -
> - tx_size = (unsigned int)mw_size / num_qps_mw;
> - qp_offset = tx_size * (qp_num / mw_count);
> -
> - qp->tx_mw_size = tx_size;
> - qp->tx_mw = nt->mw_vec[mw_num].vbase + qp_offset;
> - if (!qp->tx_mw)
> - return -EINVAL;
> -
> - qp->tx_mw_phys = mw_base + qp_offset;
> - if (!qp->tx_mw_phys)
> - return -EINVAL;
> -
> - tx_size -= sizeof(struct ntb_rx_info);
> - qp->rx_info = qp->tx_mw + tx_size;
> -
> - /* Due to housekeeping, there must be atleast 2 buffs */
> - qp->tx_max_frame = min(transport_mtu, tx_size / 2);
> - qp->tx_max_entry = tx_size / qp->tx_max_frame;
> -
> if (nt->debugfs_node_dir) {
> char debugfs_name[8];
>
> --
> 2.51.0
>