[PATCH 6.1 0628/1067] NTB: epf: Report 0-based doorbell vector via ntb_db_event()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Koichiro Den <den@valinux.co.jp>

[ Upstream commit 3147f0964cecca15e349cbfbdd6a28eb6d50379d ]

ntb_db_event() expects the vector number to be relative to the first
doorbell vector starting at 0.

Vector 0 is reserved for link events in the EPF driver, so doorbells
start at vector 1. However, both supported peers (ntb_hw_epf with
pci-epf-ntb, and pci-epf-vntb) have historically skipped vector 1 and
started doorbells at vector 2.

Pass (irq_no - 2) to ntb_db_event() so doorbells are reported as 0..N-1.
If irq_no == 1 is ever observed, warn and ignore it, since the slot is
reserved in the legacy layout and reporting it as DB#0 would collide with
the real DB#0 slot.

Fixes: 812ce2f8d14e ("NTB: Add support for EPF PCI Non-Transparent Bridge")
Suggested-by: Dave Jiang <dave.jiang@intel.com>
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: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260513024923.451765-11-den@valinux.co.jp
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/ntb/hw/epf/ntb_hw_epf.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
index b65cb77259b6e2..88f37c5c003ad0 100644
--- a/drivers/ntb/hw/epf/ntb_hw_epf.c
+++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
@@ -69,6 +69,12 @@ enum epf_ntb_bar {
 	NTB_BAR_NUM,
 };
 
+enum epf_irq_slot {
+	EPF_IRQ_LINK = 0,
+	EPF_IRQ_RESERVED_DB, /* Historically skipped slot */
+	EPF_IRQ_DB_START,
+};
+
 #define NTB_EPF_MAX_MW_COUNT	(NTB_BAR_NUM - BAR_MW1)
 
 struct ntb_epf_dev {
@@ -322,10 +328,14 @@ static irqreturn_t ntb_epf_vec_isr(int irq, void *dev)
 	irq_no = irq - ndev->irq_base;
 	ndev->db_val = irq_no + 1;
 
-	if (irq_no == 0)
+	if (irq_no == EPF_IRQ_LINK) {
 		ntb_link_event(&ndev->ntb);
-	else
-		ntb_db_event(&ndev->ntb, irq_no);
+	} else if (irq_no == EPF_IRQ_RESERVED_DB) {
+		dev_warn_ratelimited(ndev->dev,
+				     "Unexpected reserved doorbell slot IRQ received\n");
+	} else {
+		ntb_db_event(&ndev->ntb, irq_no - EPF_IRQ_DB_START);
+	}
 
 	return IRQ_HANDLED;
 }
-- 
2.53.0