Re: [PATCH v7 7/9] PCI: endpoint: pci-epf-vntb: Reuse pre-exposed doorbells and IRQ flags

On Mon, Feb 16, 2026 at 01:38:45AM +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.
>
> For embedded doorbells (e.g. interrupt-emulation), multiple doorbells
> may share a single address/data pair and a single Linux IRQ. Avoid
> requesting duplicate handlers by requesting only one IRQ in that case.
>
> Signed-off-by: Koichiro Den <[email protected]>
> ---
>  drivers/pci/endpoint/functions/pci-epf-vntb.c | 57 +++++++++++++++++--
>  1 file changed, 52 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> index 20efa27325f1..39ba4d6b7d8d 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;
>
> @@ -523,7 +528,7 @@ static int epf_ntb_db_bar_init_msi_doorbell(struct epf_ntb *ntb,
>  					    enum pci_barno barno)
>  {
>  	struct pci_epf *epf = ntb->epf;
> -	unsigned int req;
> +	unsigned int req, cnt;
>  	dma_addr_t low, high;
>  	struct msi_msg *msg;
>  	size_t sz;
> @@ -534,9 +539,29 @@ static int epf_ntb_db_bar_init_msi_doorbell(struct epf_ntb *ntb,
>  	if (ret)
>  		return ret;
>
> -	for (req = 0; req < ntb->db_count; req++) {
> +	/*
> +	 * 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 PCI_EPF_DOORBELL_EMBEDDED, the backend may provide a single MMIO
> +	 * address/data pair and a single Linux IRQ even if multiple doorbells
> +	 * were requested. Avoid requesting duplicate handlers in that case.
> +	 */
> +	cnt = ntb->db_count;
> +	if (epf->db_msg[0].type == PCI_EPF_DOORBELL_EMBEDDED)
> +		cnt = 1;

Most SoC combine all DMA channel to one irqs. But it should be not
neccessary for SoC design. It is possible each DMA channel have dedicate
irq number. I suggest check irq, instead of type.

Frank
> +
> +	for (req = 0; req < cnt; req++) {
>  		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,
> @@ -546,6 +571,22 @@ 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;
> @@ -592,6 +633,7 @@ 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;
> @@ -602,6 +644,7 @@ static int epf_ntb_db_bar_init_msi_doorbell(struct epf_ntb *ntb,
>  	while (req)
>  		free_irq(epf->db_msg[--req].virq, ntb);
>
> +err_free_doorbell:
>  	pci_epf_free_doorbell(ntb->epf);
>  	return ret;
>  }
> @@ -665,9 +708,13 @@ static void epf_ntb_db_bar_clear(struct epf_ntb *ntb)
>  	enum pci_barno barno;
>
>  	if (ntb->msi_doorbell) {
> -		int i;
> +		unsigned int cnt = ntb->db_count;
> +		unsigned int i;
>
> -		for (i = 0; i < ntb->db_count; i++)
> +		if (ntb->epf->db_msg[0].type == PCI_EPF_DOORBELL_EMBEDDED)
> +			cnt = 1;
> +
> +		for (i = 0; i < cnt; i++)
>  			free_irq(ntb->epf->db_msg[i].virq, ntb);
>  	}
>
> --
> 2.51.0
>