On Fri, Feb 27, 2026 at 05:49:50PM +0900, Koichiro Den wrote:
> Implement .db_vector_count and .db_vector_mask so ntb core/clients can map
> doorbell events to per-vector work and avoid the thundering-herd behavior.
>
> pci-epf-vntb reserves two slots in db_count: slot 0 for link events and
> slot 1 which is historically unused. Therefore the number of doorbell
> vectors is (db_count - 2).
>
> Report vectors as 0..N-1 and return BIT_ULL(db_vector) for the
> corresponding doorbell bit. While at it, use vntb_epf_db_vector_mask()
> to simplify vntb_epf_db_valid_mask().
>
> Signed-off-by: Koichiro Den <den@valinux.co.jp>
> ---
Reviewed-by: Frank Li <Frank.Li@nxp.com>
> Changes since v1:
> - No functional changes.
> - Use EPF_IRQ_DB_START instead of magic number 2, to be consistent
> with the change on Patch 8.
>
> drivers/pci/endpoint/functions/pci-epf-vntb.c | 36 +++++++++++++++++--
> 1 file changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> index b94e2e1d3421..832600b6eae1 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> @@ -1278,12 +1278,42 @@ static int vntb_epf_peer_mw_count(struct ntb_dev *ntb)
> return ntb_ndev(ntb)->num_mws;
> }
>
> +static int vntb_epf_db_vector_count(struct ntb_dev *ntb)
> +{
> + struct epf_ntb *ndev = ntb_ndev(ntb);
> +
> + /*
> + * ndev->db_count is the total number of doorbell slots exposed to
> + * the peer, including:
> + * - slot #0 reserved for link events
> + * - slot #1 historically unused (kept for protocol compatibility)
> + *
> + * Report only usable per-vector doorbell interrupts.
> + */
> + if (ndev->db_count < EPF_IRQ_DB_START)
> + return 0;
> +
> + return ndev->db_count - EPF_IRQ_DB_START;
> +}
> +
> static u64 vntb_epf_db_valid_mask(struct ntb_dev *ntb)
> {
> - if (ntb_ndev(ntb)->db_count < EPF_IRQ_DB_START)
> + return BIT_ULL(vntb_epf_db_vector_count(ntb)) - 1;
> +}
> +
> +static u64 vntb_epf_db_vector_mask(struct ntb_dev *ntb, int db_vector)
> +{
> + int nr_vec;
> +
> + /*
> + * Doorbell vectors are numbered [0 .. nr_vec - 1], where nr_vec
> + * excludes the two reserved slots described above.
> + */
> + nr_vec = vntb_epf_db_vector_count(ntb);
> + if (db_vector < 0 || db_vector >= nr_vec)
> return 0;
>
> - return BIT_ULL(ntb_ndev(ntb)->db_count - EPF_IRQ_DB_START) - 1;
> + return BIT_ULL(db_vector);
> }
>
> static int vntb_epf_db_set_mask(struct ntb_dev *ntb, u64 db_bits)
> @@ -1520,6 +1550,8 @@ static const struct ntb_dev_ops vntb_epf_ops = {
> .spad_count = vntb_epf_spad_count,
> .peer_mw_count = vntb_epf_peer_mw_count,
> .db_valid_mask = vntb_epf_db_valid_mask,
> + .db_vector_count = vntb_epf_db_vector_count,
> + .db_vector_mask = vntb_epf_db_vector_mask,
> .db_set_mask = vntb_epf_db_set_mask,
> .mw_set_trans = vntb_epf_mw_set_trans,
> .mw_clear_trans = vntb_epf_mw_clear_trans,
> --
> 2.51.0
>