Re: [PATCH 08/10] NTB: epf: Report 0-based doorbell vector via ntb_db_event()

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

On 2/24/26 6:34 AM, 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, treat it as DB#0 and emit a warning, as
> this would indicate an unexpected change in the slot layout.
> 
> 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 | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
> index ee499eaed4f3..00956ab2fbf5 100644
> --- a/drivers/ntb/hw/epf/ntb_hw_epf.c
> +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
> @@ -333,10 +333,15 @@ static irqreturn_t ntb_epf_vec_isr(int irq, void *dev)
>  	irq_no = irq - pci_irq_vector(ndev->ntb.pdev, 0);
>  	ndev->db_val = irq_no + 1;
>  
> -	if (irq_no == 0)
> +	if (irq_no == 0) {
>  		ntb_link_event(&ndev->ntb);
> -	else
> -		ntb_db_event(&ndev->ntb, irq_no);
> +	} else if (irq_no == 1) {

Given that 0 and 1 have specific meanings, maybe create a enum with appropriate naming to make it more clear. Maybe something like this or however you want to name them:

enum EPF_IRQ_SLOT {
	EPF_IRQ_LINK = 0,
	EPF_IRQ_RESERVED_DB,
	EPF_IRQ_DB_START,
};
> +		dev_warn_ratelimited(ndev->dev,
> +				     "Unexpected irq_no 1 received. Treat it as DB#0.\n");
> +		ntb_db_event(&ndev->ntb, 0);
> +	} else {
> +		ntb_db_event(&ndev->ntb, irq_no - 2);

And then here you can do
ntb_db_event(&ndev->ntb, irq_no - EPF_IRQ_DB_START);

> +	}
>  
>  	return IRQ_HANDLED;
>  }