[RFC PATCH v4 17/38] NTB: ntb_transport: Dynamically determine qp count

Koichiro Den
2026-01-18T13:55:30Z

One MW can host multiple queue pairs, so stop limiting qp_count to the
number of MWs.

Now that both TX and RX MW sizing are done in the same place, the MW
layout is derived from a single code path on both host and endpoint, so
the layout cannot diverge between the two sides.

Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
drivers/ntb/ntb_transport.c | 26 +++++++++++++++++++++++---
1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
index 57a21f2daac6..6ed680d0470f 100644
--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -1022,7 +1022,9 @@ static void ntb_transport_link_work(struct work_struct *work)
container_of(work, struct ntb_transport_ctx, link_work.work);
struct ntb_dev *ndev = nt->ndev;
struct pci_dev *pdev = ndev->pdev;
+ struct ntb_transport_qp *qp;
resource_size_t size;
+ u64 qp_bitmap_free;
u32 val;
int rc = 0, i, spad;

@@ -1070,8 +1072,28 @@ static void ntb_transport_link_work(struct work_struct *work)

val = ntb_spad_read(ndev, NUM_QPS);
dev_dbg(&pdev->dev, "Remote max number of qps = %d\n", val);
- if (val != nt->qp_count)
+ if (val == 0) {
goto out;
+ } else if (val < nt->qp_count) {
+ /*
+ * Clamp local qp_count to peer-advertised NUM_QPS to avoid
+ * mismatched queues.
+ */
+ qp_bitmap_free = nt->qp_bitmap_free;
+ for (i = val; i < nt->qp_count; i++) {
+ qp = &nt->qp_vec[i];
+ ntb_transport_free_queue(qp);
+ debugfs_remove_recursive(qp->debugfs_dir);
+
+ /* Do not expose the queue any longer */
+ nt->qp_bitmap &= ~BIT_ULL(i);
+ nt->qp_bitmap_free &= ~BIT_ULL(i);
+ }
+ dev_warn(&pdev->dev,
+ "Local number of qps is reduced: %d->%d (%#llx->%#llx)\n",
+ nt->qp_count, val, qp_bitmap_free, nt->qp_bitmap_free);
+ nt->qp_count = val;
+ }

val = ntb_spad_read(ndev, NUM_MWS);
dev_dbg(&pdev->dev, "Remote number of mws = %d\n", val);
@@ -1300,8 +1322,6 @@ static int ntb_transport_probe(struct ntb_client *self, struct ntb_dev *ndev)

if (max_num_clients && max_num_clients < qp_count)
qp_count = max_num_clients;
- else if (nt->mw_count < qp_count)
- qp_count = nt->mw_count;

qp_bitmap &= BIT_ULL(qp_count) - 1;

--
2.51.0