Re: [PATCH v4 10/12] NTB: epf: Report 0-based doorbell vector via ntb_db_event()

[Frank Li]

On Wed, May 13, 2026 at 11:49:21AM +0900, Koichiro Den wrote:
> ntb_db_event() expects the vector number to be relative to the first
> doorbell vector starting at 0.
>
> Vector 0 is reserved for link events in the EPF driver, so doorbells
> start at vector 1. However, both supported peers (ntb_hw_epf with
> pci-epf-ntb, and pci-epf-vntb) have historically skipped vector 1 and
> started doorbells at vector 2.
>
> Pass (irq_no - 2) to ntb_db_event() so doorbells are reported as 0..N-1.
> If irq_no == 1 is ever observed, warn and ignore it, since the slot is
> reserved in the legacy layout and reporting it as DB#0 would collide with
> the real DB#0 slot.
>
> Fixes: 812ce2f8d14e ("NTB: Add support for EPF PCI Non-Transparent Bridge")
> Suggested-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

> Changes since v3:
>   - Ignore the reserved legacy slot instead of reporting it as DB#0.
>   - Drop a Reviewed-by tag due to the behavior change.
>
>  drivers/ntb/hw/epf/ntb_hw_epf.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
> index c0bab3292075..7b0fc7ef00c6 100644
> --- a/drivers/ntb/hw/epf/ntb_hw_epf.c
> +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
> @@ -81,6 +81,12 @@ enum epf_ntb_bar {
>  	NTB_BAR_NUM,
>  };
>
> +enum epf_irq_slot {
> +	EPF_IRQ_LINK = 0,
> +	EPF_IRQ_RESERVED_DB, /* Historically skipped slot */
> +	EPF_IRQ_DB_START,
> +};
> +
>  #define NTB_EPF_MAX_MW_COUNT	(NTB_BAR_NUM - BAR_MW1)
>
>  struct ntb_epf_dev {
> @@ -334,10 +340,14 @@ static irqreturn_t ntb_epf_vec_isr(int irq, void *dev)
>  	irq_no = irq - ndev->irq_base;
>  	ndev->db_val = irq_no + 1;
>
> -	if (irq_no == 0)
> +	if (irq_no == EPF_IRQ_LINK) {
>  		ntb_link_event(&ndev->ntb);
> -	else
> -		ntb_db_event(&ndev->ntb, irq_no);
> +	} else if (irq_no == EPF_IRQ_RESERVED_DB) {
> +		dev_warn_ratelimited(ndev->dev,
> +				     "Unexpected reserved doorbell slot IRQ received\n");
> +	} else {
> +		ntb_db_event(&ndev->ntb, irq_no - EPF_IRQ_DB_START);
> +	}
>
>  	return IRQ_HANDLED;
>  }
> --
> 2.51.0
>