[PATCH 08/10] NTB: epf: Report 0-based doorbell vector via ntb_db_event()

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, treat it as DB#0 and emit a warning, as
this would indicate an unexpected change in the slot layout.

Fixes: 812ce2f8d14e ("NTB: Add support for EPF PCI Non-Transparent Bridge")
Signed-off-by: Koichiro Den <[email protected]>
---
 drivers/ntb/hw/epf/ntb_hw_epf.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
index ee499eaed4f3..00956ab2fbf5 100644
--- a/drivers/ntb/hw/epf/ntb_hw_epf.c
+++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
@@ -333,10 +333,15 @@ static irqreturn_t ntb_epf_vec_isr(int irq, void *dev)
 	irq_no = irq - pci_irq_vector(ndev->ntb.pdev, 0);
 	ndev->db_val = irq_no + 1;
 
-	if (irq_no == 0)
+	if (irq_no == 0) {
 		ntb_link_event(&ndev->ntb);
-	else
-		ntb_db_event(&ndev->ntb, irq_no);
+	} else if (irq_no == 1) {
+		dev_warn_ratelimited(ndev->dev,
+				     "Unexpected irq_no 1 received. Treat it as DB#0.\n");
+		ntb_db_event(&ndev->ntb, 0);
+	} else {
+		ntb_db_event(&ndev->ntb, irq_no - 2);
+	}
 
 	return IRQ_HANDLED;
 }
-- 
2.51.0