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Message-ID: <aS30YHfDUH7mRheL@lizhi-Precision-Tower-5810>
Date: Mon, 1 Dec 2025 15:02:40 -0500
From: Frank Li <Frank.li@....com>
To: Koichiro Den <den@...inux.co.jp>
Cc: ntb@...ts.linux.dev, linux-pci@...r.kernel.org,
dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
mani@...nel.org, kwilczynski@...nel.org, kishon@...nel.org,
bhelgaas@...gle.com, corbet@....net, vkoul@...nel.org,
jdmason@...zu.us, dave.jiang@...el.com, allenbh@...il.com,
Basavaraj.Natikar@....com, Shyam-sundar.S-k@....com,
kurt.schwemmer@...rosemi.com, logang@...tatee.com,
jingoohan1@...il.com, lpieralisi@...nel.org, robh@...nel.org,
jbrunet@...libre.com, fancer.lancer@...il.com, arnd@...db.de,
pstanner@...hat.com, elfring@...rs.sourceforge.net
Subject: Re: [RFC PATCH v2 14/27] NTB: ntb_transport: Move TX memory window
setup into setup_qp_mw()
On Sun, Nov 30, 2025 at 01:03:52AM +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 relaxing 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 behaviour, while preparing for relaxing the
> qp_count limitation and improving readibility.
>
> No functional change is intended.
>
> Signed-off-by: Koichiro Den <den@...inux.co.jp>
> ---
> drivers/ntb/ntb_transport.c | 67 ++++++++++++++-----------------------
> 1 file changed, 26 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
> index 57b4c0511927..79063e2f911b 100644
> --- a/drivers/ntb/ntb_transport.c
> +++ b/drivers/ntb/ntb_transport.c
> @@ -569,7 +569,8 @@ 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;
> + unsigned int num_qps_mw;
> + unsigned int mw_size, mw_size_per_qp, qp_offset, rx_info_offset;
> unsigned int mw_num, mw_count, qp_count;
> unsigned int i;
> int node;
> @@ -588,15 +589,33 @@ 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_size = min(nt->mw_vec[mw_num].phys_size, mw->xlat_size);
> + if (max_mw_size && mw_size > max_mw_size)
> + mw_size = max_mw_size;
>
> - qp->remote_rx_info = qp->rx_buff + rx_size;
> + /* Split this MW evenly among the queue pairs mapped to it. */
> + mw_size_per_qp = (unsigned int)mw_size / num_qps_mw;
Can you use the same variable firstly to make review easily?
tx_size = (unsigned int)mw_size / num_qps_mw;
It is hard to make sure code logic is the same as old one.
Frank
> + qp_offset = mw_size_per_qp * (qp_num / mw_count);
> +
> + /* Place remote_rx_info at the end of the per-QP region. */
> + rx_info_offset = mw_size_per_qp - sizeof(struct ntb_rx_info);
> +
> + qp->tx_mw_size = mw_size_per_qp;
> + qp->tx_mw = nt->mw_vec[mw_num].vbase + qp_offset;
> + if (!qp->tx_mw)
> + return -EINVAL;
> + qp->tx_mw_phys = nt->mw_vec[mw_num].phys_addr + qp_offset;
> + if (!qp->tx_mw_phys)
> + return -EINVAL;
> + qp->rx_info = qp->tx_mw + rx_info_offset;
> + qp->rx_buff = mw->virt_addr + qp_offset;
> + qp->remote_rx_info = qp->rx_buff + rx_info_offset;
>
> /* Due to housekeeping, there must be atleast 2 buffs */
> - qp->rx_max_frame = min(transport_mtu, rx_size / 2);
> - qp->rx_max_entry = rx_size / qp->rx_max_frame;
> + qp->tx_max_frame = min(transport_mtu, mw_size_per_qp / 2);
> + qp->tx_max_entry = mw_size_per_qp / qp->tx_max_frame;
> + qp->rx_max_frame = min(transport_mtu, mw_size_per_qp / 2);
> + qp->rx_max_entry = mw_size_per_qp / qp->rx_max_frame;
> qp->rx_index = 0;
>
> /*
> @@ -1133,11 +1152,7 @@ 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;
> @@ -1152,36 +1167,6 @@ 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];
>
> --
> 2.48.1
>
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