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

[Dave Jiang]

On 5/12/26 7:49 PM, 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")
> Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>

Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>


> ---
> 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);
>