From: Koichiro Den <den@valinux.co.jp>
To: "Jon Mason" <jdmason@kudzu.us>,
"Dave Jiang" <dave.jiang@intel.com>,
"Allen Hubbe" <allenbh@gmail.com>,
"Manivannan Sadhasivam" <mani@kernel.org>,
"Krzysztof Wilczyński" <kwilczynski@kernel.org>,
"Kishon Vijay Abraham I" <kishon@kernel.org>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Frank Li" <Frank.Li@nxp.com>,
"Jerome Brunet" <jbrunet@baylibre.com>,
"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
"Niklas Cassel" <cassel@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
ntb@lists.linux.dev
Subject: [PATCH v4 07/12] PCI: endpoint: pci-epf-vntb: Implement db_vector_count/mask for doorbells
Date: Wed, 13 May 2026 11:49:18 +0900 [thread overview]
Message-ID: <20260513024923.451765-8-den@valinux.co.jp> (raw)
In-Reply-To: <20260513024923.451765-1-den@valinux.co.jp>
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>
---
Changes since v3:
- Tighten db_count-derived mask handling after Sashiko pointed out
invalid-shift cases. The new configfs guards should prevent them, but
keep the helpers robust on their own.
- Drop Reviewed-by tag due to the added validation.
drivers/pci/endpoint/functions/pci-epf-vntb.c | 42 ++++++++++++++++++-
1 file changed, 40 insertions(+), 2 deletions(-)
diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
index 58e41d95d029..c3caec927d74 100644
--- 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,
--
2.51.0
next prev parent reply other threads:[~2026-05-13 2:49 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-13 2:49 [PATCH v4 00/12] PCI: endpoint: pci-epf-vntb / NTB: epf: Enable per-doorbell bit handling Koichiro Den
2026-05-13 2:49 ` [PATCH v4 01/12] PCI: endpoint: pci-epf-vntb: Document legacy MSI doorbell offset Koichiro Den
2026-05-13 2:49 ` [PATCH v4 02/12] PCI: endpoint: pci-epf-vntb: Defer pci_epc_raise_irq() out of atomic context Koichiro Den
2026-05-14 18:53 ` Frank Li
2026-05-13 2:49 ` [PATCH v4 03/12] PCI: endpoint: pci-epf-vntb: Report 0-based doorbell vector via ntb_db_event() Koichiro Den
2026-05-13 2:49 ` [PATCH v4 04/12] PCI: endpoint: pci-epf-vntb: Reject unusable doorbell counts Koichiro Den
2026-05-14 18:55 ` Frank Li
2026-05-13 2:49 ` [PATCH v4 05/12] PCI: endpoint: pci-epf-vntb: Guard configfs writes after EPC attach Koichiro Den
2026-05-14 18:57 ` Frank Li
2026-05-13 2:49 ` [PATCH v4 06/12] PCI: endpoint: pci-epf-vntb: Exclude reserved slots from db_valid_mask Koichiro Den
2026-05-13 2:49 ` Koichiro Den [this message]
2026-05-14 19:02 ` [PATCH v4 07/12] PCI: endpoint: pci-epf-vntb: Implement db_vector_count/mask for doorbells Frank Li
2026-05-13 2:49 ` [PATCH v4 08/12] NTB: epf: Document legacy doorbell slot offset in ntb_epf_peer_db_set() Koichiro Den
2026-05-13 2:49 ` [PATCH v4 09/12] NTB: epf: Make db_valid_mask cover only real doorbell bits Koichiro Den
2026-05-26 22:21 ` Dave Jiang
2026-05-13 2:49 ` [PATCH v4 10/12] NTB: epf: Report 0-based doorbell vector via ntb_db_event() Koichiro Den
2026-05-14 19:03 ` Frank Li
2026-05-26 22:28 ` Dave Jiang
2026-05-13 2:49 ` [PATCH v4 11/12] NTB: epf: Fix doorbell bitmask and IRQ vector handling Koichiro Den
2026-05-14 19:06 ` Frank Li
2026-05-26 22:36 ` Dave Jiang
2026-05-13 2:49 ` [PATCH v4 12/12] NTB: epf: Implement db_vector_count/mask for doorbells Koichiro Den
2026-05-26 22:47 ` Dave Jiang
2026-06-23 16:31 ` Bjorn Helgaas
2026-06-24 1:35 ` Koichiro Den
2026-05-19 14:42 ` [PATCH v4 00/12] PCI: endpoint: pci-epf-vntb / NTB: epf: Enable per-doorbell bit handling Manivannan Sadhasivam
2026-05-19 21:29 ` Dave Jiang
2026-05-21 6:29 ` Koichiro Den
2026-05-26 14:45 ` Dave Jiang
2026-05-26 15:56 ` Koichiro Den
2026-05-26 16:27 ` Dave Jiang
2026-05-27 9:09 ` Manivannan Sadhasivam
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