Re: [RFC PATCH 1/2] pci: Allow platforms to modify BAR adresses

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.04.2026 09:57, Mykyta Poturai wrote:
> This patch is a preparatory work for adding Region ID support on Renesas
> R-Car series boards. Add new host bridge op "fixup_bar" that allows
> platforms to modify BAR addresses before they are mapped.
> 
> Because x86 don't have support for PCI Host Bridge drivers, add another
> level of indirection in form of platform_pci_fixup_bar() function, that
> will call host bridge op on ARM and do nothing on x86.
> 
> Signed-off-by: Mykyta Poturai <mykyta_poturai@xxxxxxxx>
> ---
>  xen/arch/arm/include/asm/pci.h  |  3 +++
>  xen/arch/arm/include/asm/vpci.h |  9 +++++++++
>  xen/arch/arm/vpci.c             | 12 ++++++++++++
>  xen/arch/x86/include/asm/vpci.h |  6 ++++++
>  xen/drivers/vpci/header.c       |  2 ++
>  5 files changed, 32 insertions(+)
> 
> diff --git a/xen/arch/arm/include/asm/pci.h b/xen/arch/arm/include/asm/pci.h
> index 7c3211823f..398a4eb746 100644
> --- a/xen/arch/arm/include/asm/pci.h
> +++ b/xen/arch/arm/include/asm/pci.h
> @@ -80,6 +80,9 @@ struct pci_ops {
>      void (*init_bus_range)(struct dt_device_node *dev,
>                             struct pci_host_bridge *bridge,
>                             struct pci_config_window *cfg);
> +    void (*fixup_bar)(struct pci_host_bridge *bridge,
> +                      unsigned int bar_num,
> +                      paddr_t *addr);

I'm not an Arm maintainer, but if such a hook - used only when a certain
CONFIG_* is active, as per patch 2 - was introduced in common or x86 code,
I'd ask for the hook to also be conditional. Doing so avoids accidental use
without ...

> --- a/xen/arch/arm/vpci.c
> +++ b/xen/arch/arm/vpci.c
> @@ -189,6 +189,18 @@ unsigned int domain_vpci_get_num_mmio_handlers(struct 
> domain *d)
>      return 1;
>  }
>  
> +void platform_pci_fixup_bar(const struct pci_dev *pdev,
> +                                          unsigned int bar_num,
> +                                          paddr_t *addr)
> +{
> +    struct pci_host_bridge *bridge = pci_find_host_bridge(pdev->sbdf.seg, 
> pdev->sbdf.bus);
> +
> +    if ( bridge->ops->fixup_bar )
> +    {
> +        bridge->ops->fixup_bar(bridge, bar_num, addr);
> +    }

... such a conditional around it.

Jan