[PATCH v4 09/12] NTB: epf: Make db_valid_mask cover only real doorbell bits

ndev->db_count includes an unused doorbell slot due to the legacy extra
offset in the peer doorbell path. db_valid_mask must cover only the real
doorbell bits and exclude the unused slot.

Set db_valid_mask to BIT_ULL(db_count - 1) - 1.

Fixes: 812ce2f8d14e ("NTB: Add support for EPF PCI Non-Transparent Bridge")
Reviewed-by: Frank Li <[email protected]>
Signed-off-by: Koichiro Den <[email protected]>
---
Changes since v3:
  - Drop the post-init db_count lower-bound check; ntb_epf_init_isr()
    already requests at least NTB_EPF_MIN_DB_COUNT + 1 vectors.

 drivers/ntb/hw/epf/ntb_hw_epf.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
index 21d942824983..c0bab3292075 100644
--- a/drivers/ntb/hw/epf/ntb_hw_epf.c
+++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
@@ -580,7 +580,11 @@ static int ntb_epf_init_dev(struct ntb_epf_dev *ndev)
 		return ret;
 	}
 
-	ndev->db_valid_mask = BIT_ULL(ndev->db_count) - 1;
+	/*
+	 * ndev->db_count includes an extra skipped slot due to the legacy
+	 * doorbell layout, hence -1.
+	 */
+	ndev->db_valid_mask = BIT_ULL(ndev->db_count - 1) - 1;
 	ndev->mw_count = readl(ndev->ctrl_reg + NTB_EPF_MW_COUNT);
 	ndev->spad_count = readl(ndev->ctrl_reg + NTB_EPF_SPAD_COUNT);
 
-- 
2.51.0