[PATCH v4 04/12] PCI: endpoint: pci-epf-vntb: Reject unusable doorbell counts

pci-epf-vntb reserves slot 0 for link events and keeps slot 1 unused for
legacy layout compatibility. A db_count smaller than MIN_DB_COUNT leaves
no usable doorbell slot after those reservations.

Reject such configurations when configuring interrupts.

While at it, move MAX_DB_COUNT next to MIN_DB_COUNT. They are used as a
pair in the range check, and keeping them together makes the valid doorbell
range easier to read.

Signed-off-by: Koichiro Den <[email protected]>
---
Changes since v3:
  - New patch.

 drivers/pci/endpoint/functions/pci-epf-vntb.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
index d31e2eee0869..818ae5999976 100644
--- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
+++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
@@ -67,7 +67,6 @@ static struct workqueue_struct *kpcintb_workqueue;
 #define NTB_MW_OFFSET			2
 #define DB_COUNT_MASK			GENMASK(15, 0)
 #define MSIX_ENABLE			BIT(16)
-#define MAX_DB_COUNT			32
 #define MAX_MW				4
 
 /* Limit per-work execution to avoid monopolizing kworker on doorbell storms. */
@@ -89,6 +88,9 @@ enum epf_irq_slot {
 	EPF_IRQ_DB_START,
 };
 
+#define MIN_DB_COUNT			(EPF_IRQ_DB_START + 1)
+#define MAX_DB_COUNT			32
+
 /*
  * +--------------------------------------------------+ Base
  * |                                                  |
@@ -512,9 +514,9 @@ static int epf_ntb_configure_interrupt(struct epf_ntb *ntb)
 		return -EINVAL;
 	}
 
-	if (!ntb->db_count || ntb->db_count > MAX_DB_COUNT) {
-		dev_err(dev, "DB count %d out of range (1 - %d)\n",
-			ntb->db_count, MAX_DB_COUNT);
+	if (ntb->db_count < MIN_DB_COUNT || ntb->db_count > MAX_DB_COUNT) {
+		dev_err(dev, "DB count %d out of range (%d - %d)\n",
+			ntb->db_count, MIN_DB_COUNT, MAX_DB_COUNT);
 		return -EINVAL;
 	}
 
-- 
2.51.0