Re: [PATCH v13 7/7] PCI: endpoint: pci-ep-msi: Add embedded doorbell fallback

On Tue, Apr 07, 2026 at 12:57:17AM +0900, Koichiro Den wrote:
> Some endpoint platforms cannot use platform MSI / GIC ITS to implement
> EP-side doorbells. In those cases, EPF drivers cannot provide an
> interrupt-driven doorbell and often fall back to polling.
>
> Add an "embedded" doorbell backend that uses a controller-integrated
> doorbell target (e.g. DesignWare integrated eDMA interrupt-emulation
> doorbell).
>
> The backend locates the doorbell register and a corresponding Linux IRQ
> via the EPC aux-resource API. If the doorbell register is already
> exposed via a fixed BAR mapping, provide BAR+offset. Otherwise provide
> the DMA address returned by dma_map_resource() (which may be an IOVA
> when an IOMMU is enabled) so EPF drivers can map it into BAR space.
>
> When MSI doorbell allocation fails with -ENODEV,
> pci_epf_alloc_doorbell() falls back to this embedded backend.
>
> Suggested-by: Manivannan Sadhasivam <[email protected]>
> Signed-off-by: Koichiro Den <[email protected]>
> ---
>
...
> +static int pci_epf_alloc_doorbell_embedded(struct pci_epf *epf, u16 num_db)
> +{
> +	const struct pci_epc_aux_resource *doorbell = NULL;
> +	struct pci_epf_doorbell_msg *msg;
> +	struct pci_epc *epc = epf->epc;
> +	size_t map_size = 0, off = 0;
> +	dma_addr_t iova_base = 0;
> +	phys_addr_t phys_base;
> +	int count, ret, i;
> +	u64 addr;
> +
> +	count = pci_epc_get_aux_resources_count(epc, epf->func_no,
> +						epf->vfunc_no);
> +	if (count == -EOPNOTSUPP)
> +		return -ENODEV;

why need replace error code here ?


Frank