Re: [PATCH v4 3/4] xen/arm: add support for PCI child bus

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 23 Apr 2025, Mykyta Poturai wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> 
> PCI host bridges often have different ways to access the root and child
> bus configuration spaces. One of the examples is Designware's host bridge
> and its multiple clones [1].
> 
> Linux kernel implements this by instantiating a child bus when device
> drivers provide not only the usual pci_ops to access ECAM space (this is
> the case for the generic host bridge), but also means to access the child
> bus which has a dedicated configuration space and own implementation for
> accessing the bus, e.g. child_ops.
> 
> For Xen it is not feasible to fully implement PCI bus infrastructure as
> Linux kernel does, but still child bus can be supported.
> 
> Add support for the PCI child bus which includes the following changes:
> - introduce bus mapping functions depending on SBDF
> - assign bus start and end for the child bus and re-configure the same for
>   the parent (root) bus
> - make pci_find_host_bridge be aware of multiple busses behind the same bridge
> - update pci_host_bridge_mappings, so it also doesn't map to guest the memory
>   spaces belonging to the child bus
> - make pci_host_common_probe accept one more pci_ops structure for the child 
> bus
> - install MMIO handlers for the child bus
> - re-work vpci_mmio_{write|read} with parent and child approach in mind
> 
> [1] https://elixir.bootlin.com/linux/v5.15/source/drivers/pci/controller/dwc
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> Signed-off-by: Mykyta Poturai <mykyta_poturai@xxxxxxxx>

I just wanted to say that pending Stewart's comment, this patch looks
good to me