Re: [PATCH v10 7/7] PCI: endpoint: pci-ep-msi: Add embedded doorbell fallback

[Niklas Cassel]

On Mon, Mar 02, 2026 at 04:14:27PM +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.
> 
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> ---

Tested-by: Niklas Cassel <cassel@xxxxxxxxxx>