Re: [PATCH v2 07/10] NTB: epf: Make db_valid_mask cover only real doorbell bits

[Frank Li]

On Fri, Feb 27, 2026 at 05:49:52PM +0900, Koichiro Den wrote:
> 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")
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> ---
Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> Changes since v1:
>   - No functional changes.
>   - Addressed review comments (documentation).
>
>  drivers/ntb/hw/epf/ntb_hw_epf.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
> index bce7130fec39..07dc97d3270b 100644
> --- a/drivers/ntb/hw/epf/ntb_hw_epf.c
> +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
> @@ -580,7 +580,17 @@ static int ntb_epf_init_dev(struct ntb_epf_dev *ndev)
>  		return ret;
>  	}
>
> -	ndev->db_valid_mask = BIT_ULL(ndev->db_count) - 1;
> +	if (ndev->db_count < NTB_EPF_MIN_DB_COUNT) {
> +		dev_err(dev, "db_count %u is less than %u\n", ndev->db_count,
> +			NTB_EPF_MIN_DB_COUNT);
> +		return -EINVAL;
> +	}
> +
> +	/*
> +	 * 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
>