Re: [PATCH 3/3] PCI: endpoint: pci-ep-msi: Let non-first EPFs use embedded doorbells

On Wed, Jul 29, 2026 at 02:23:06AM +0900, Koichiro Den wrote:
> pci_epf_alloc_doorbell() rejects every EPF that is not the first one
> attached to the EPC because the MSI-backed path can populate doorbell
> messages only for that EPF. This also prevents non-first EPFs from using
> the embedded doorbell backend.
>
> Keep the MSI-backed path limited to the first attached EPF. Let
> non-first EPFs skip it and try the embedded doorbell directly. The
> embedded IRQ is exclusive, so a second embedded user fails to request
> the IRQ instead of receiving another EPF's notifications.
>
> Signed-off-by: Koichiro Den <[email protected]>
> ---

Reviewed-by: Frank Li <[email protected]>

>  drivers/pci/endpoint/pci-ep-msi.c | 31 +++++++++++++++++--------------
>  1 file changed, 17 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/pci/endpoint/pci-ep-msi.c b/drivers/pci/endpoint/pci-ep-msi.c
> index a123a189b4e6..5ea7eef9794f 100644
> --- a/drivers/pci/endpoint/pci-ep-msi.c
> +++ b/drivers/pci/endpoint/pci-ep-msi.c
> @@ -199,28 +199,31 @@ static int pci_epf_alloc_doorbell_msi(struct pci_epf *epf, u16 num_db)
>  int pci_epf_alloc_doorbell(struct pci_epf *epf, u16 num_db)
>  {
>  	struct pci_epc *epc = epf->epc;
> +	struct pci_epf *first_epf;
>  	struct device *dev = &epf->dev;
>  	int ret;
>
> -	/* TODO: Multi-EPF support */
> -	if (list_first_entry_or_null(&epc->pci_epf, struct pci_epf, list) != epf) {
> -		dev_err(dev, "Doorbell doesn't support multiple EPF\n");
> -		return -EINVAL;
> -	}
> -
>  	if (epf->db_msg)
>  		return -EBUSY;
>
> -	ret = pci_epf_alloc_doorbell_msi(epf, num_db);
> -	if (!ret)
> -		return 0;
> -
>  	/*
> -	 * Fall back to embedded doorbell only when platform MSI is unavailable
> -	 * for this EPC.
> +	 * The MSI-backed doorbell path currently targets the first EPF attached
> +	 * to the EPC. Let non-first EPFs try the embedded doorbell instead.
>  	 */
> -	if (ret != -ENODEV)
> -		return ret;
> +	first_epf = list_first_entry_or_null(&epc->pci_epf, struct pci_epf,
> +					     list);
> +	if (first_epf == epf) {
> +		ret = pci_epf_alloc_doorbell_msi(epf, num_db);
> +		if (!ret)
> +			return 0;
> +
> +		/*
> +		 * Fall back to embedded doorbell only when platform MSI is
> +		 * unavailable for this EPC.
> +		 */
> +		if (ret != -ENODEV)
> +			return ret;
> +	}
>
>  	ret = pci_epf_alloc_doorbell_embedded(epf, num_db);
>  	if (ret) {
> --
> 2.51.0
>