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

[Dave Jiang <dave.jiang@intel.com>]

On 2/24/26 6:34 AM, 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@valinux.co.jp>
> ---
>  drivers/ntb/hw/epf/ntb_hw_epf.c | 8 +++++++-
>  1 file changed, 7 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..ee499eaed4f3 100644
> --- a/drivers/ntb/hw/epf/ntb_hw_epf.c
> +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
> @@ -580,7 +580,13 @@ 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_valid_mask = BIT_ULL(ndev->db_count - 1) - 1;

I would suggest adding a comment in the code for why this is for future readers.

DJ

>  	ndev->mw_count = readl(ndev->ctrl_reg + NTB_EPF_MW_COUNT);
>  	ndev->spad_count = readl(ndev->ctrl_reg + NTB_EPF_SPAD_COUNT);
>