Re: [PATCH v8 7/9] PCI: endpoint: pci-epf-vntb: Reuse pre-exposed doorbells and IRQ flags

[Frank Li]

On Tue, Feb 17, 2026 at 05:05:59PM +0900, Koichiro Den wrote:
> Support doorbell backends where the doorbell target is already exposed
> via a platform-owned fixed BAR mapping and/or where the doorbell IRQ
> must be requested with specific flags.
>
> When pci_epf_alloc_doorbell() provides db_msg[].bar/offset, reuse the
> pre-exposed BAR window and skip programming a new inbound mapping. Also
> honor db_msg[].irq_flags when requesting the doorbell IRQ.
>
> Multiple doorbells may share the same Linux IRQ. Avoid duplicate
> request_irq() calls by requesting each unique virq once.
>
> This makes pci-epf-vntb work with platform-defined or embedded doorbell

Nit: Make pci-epf-vntb work with ...

> backends without exposing backend-specific details to the consumer
> layer.
>
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> ---
> Changes since v7:
>   - Deduplicate request_irq()/free_irq() calls based on virq (shared
>     IRQ) rather than doorbell type.
>
>  drivers/pci/endpoint/functions/pci-epf-vntb.c | 61 ++++++++++++++++++-
>  1 file changed, 58 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> index 52cf442ca1d9..b1e8414c4e43 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> @@ -134,6 +134,11 @@ struct epf_ntb {
>  	u16 vntb_vid;
>
>  	bool linkup;
> +
> +	/*
> +	 * True when doorbells are interrupt-driven (MSI or embedded), false
> +	 * when polled.
> +	 */
>  	bool msi_doorbell;
>  	u32 spad_size;
>
> @@ -517,6 +522,17 @@ static int epf_ntb_configure_interrupt(struct epf_ntb *ntb)
>  	return 0;
>  }
>
> +static bool epf_ntb_db_irq_is_first(const struct pci_epf *epf, unsigned int idx)

epf_ntb_db_irq_is_duplicated() look better, below 'if' needn't !

Frank

> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < idx; i++)
> +		if (epf->db_msg[i].virq == epf->db_msg[idx].virq)
> +			return false;
> +
> +	return true;
> +}
> +
>  static int epf_ntb_db_bar_init_msi_doorbell(struct epf_ntb *ntb,
>  					    struct pci_epf_bar *db_bar,
>  					    const struct pci_epc_features *epc_features,
> @@ -533,9 +549,24 @@ static int epf_ntb_db_bar_init_msi_doorbell(struct epf_ntb *ntb,
>  	if (ret)
>  		return ret;
>
> +	/*
> +	 * The doorbell target may already be exposed by a platform-owned fixed
> +	 * BAR. In that case, we must reuse it and the requested db_bar must
> +	 * match.
> +	 */
> +	if (epf->db_msg[0].bar != NO_BAR && epf->db_msg[0].bar != barno) {
> +		ret = -EINVAL;
> +		goto err_free_doorbell;
> +	}
> +
>  	for (req = 0; req < ntb->db_count; req++) {
> +		/* Avoid requesting duplicate handlers */
> +		if (!epf_ntb_db_irq_is_first(epf, req))
> +			continue;
> +
>  		ret = request_irq(epf->db_msg[req].virq, epf_ntb_doorbell_handler,
> -				  0, "pci_epf_vntb_db", ntb);
> +				  epf->db_msg[req].irq_flags, "pci_epf_vntb_db",
> +				  ntb);
>
>  		if (ret) {
>  			dev_err(&epf->dev,
> @@ -545,6 +576,22 @@ static int epf_ntb_db_bar_init_msi_doorbell(struct epf_ntb *ntb,
>  		}
>  	}
>
> +	if (epf->db_msg[0].bar != NO_BAR) {
> +		for (i = 0; i < ntb->db_count; i++) {
> +			msg = &epf->db_msg[i].msg;
> +
> +			if (epf->db_msg[i].bar != barno) {
> +				ret = -EINVAL;
> +				goto err_free_irq;
> +			}
> +
> +			ntb->reg->db_data[i] = msg->data;
> +			ntb->reg->db_offset[i] = epf->db_msg[i].offset;
> +		}
> +		goto out;
> +	}
> +
> +	/* Program inbound mapping for the doorbell */
>  	msg = &epf->db_msg[0].msg;
>
>  	high = 0;
> @@ -591,6 +638,7 @@ static int epf_ntb_db_bar_init_msi_doorbell(struct epf_ntb *ntb,
>  		ntb->reg->db_offset[i] = offset;
>  	}
>
> +out:
>  	ntb->reg->db_entry_size = 0;
>
>  	ntb->msi_doorbell = true;
> @@ -598,9 +646,13 @@ static int epf_ntb_db_bar_init_msi_doorbell(struct epf_ntb *ntb,
>  	return 0;
>
>  err_free_irq:
> -	for (req--; req >= 0; req--)
> +	for (req--; req >= 0; req--) {
> +		if (!epf_ntb_db_irq_is_first(epf, req))
> +			continue;
>  		free_irq(epf->db_msg[req].virq, ntb);
> +	}
>
> +err_free_doorbell:
>  	pci_epf_free_doorbell(ntb->epf);
>  	return ret;
>  }
> @@ -666,8 +718,11 @@ static void epf_ntb_db_bar_clear(struct epf_ntb *ntb)
>  	if (ntb->msi_doorbell) {
>  		int i;
>
> -		for (i = 0; i < ntb->db_count; i++)
> +		for (i = 0; i < ntb->db_count; i++) {
> +			if (!epf_ntb_db_irq_is_first(ntb->epf, i))
> +				continue;
>  			free_irq(ntb->epf->db_msg[i].virq, ntb);
> +		}
>  	}
>
>  	if (ntb->epf->db_msg)
> --
> 2.51.0
>