PCI: endpoint: pci-epf-vntb: Implement .db_vector_count()/mask() for doorbells

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. Build db_valid_mask from a validated vector
count so out-of-range db_count values cannot create invalid shifts.

Signed-off-by: Koichiro Den <den@valinux.co.jp>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260513024923.451765-8-den@valinux.co.jp

diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
index 58e41d95d029c02a31dceadb6407d9309a26adc2..c3caec927d74886236ef77420cba3bebe12f23ca 100644 (file)
--- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
+++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
@@ -1362,12 +1362,48 @@ 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);
+       u32 db_count = READ_ONCE(ndev->db_count);
+
+       /*
+        * 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 (db_count < MIN_DB_COUNT || db_count > MAX_DB_COUNT)
+               return 0;
+
+       return 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)
+       int nr_vec = vntb_epf_db_vector_count(ntb);
+
+       if (!nr_vec)
+               return 0;
+
+       return GENMASK_ULL(nr_vec - 1, 0);
+}
+
+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)
@@ -1617,6 +1653,8 @@ 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,