Re: [RFC PATCH v1 1/4] arm/pci: PCI setup and PCI host bridge discovery within XEN on ARM.

[Rahul Singh <Rahul.Singh@arm.com>]

> On 24 Jul 2020, at 9:05 am, Julien Grall <julien@xen.org> wrote:
> 
> Hi,
> 
> On 24/07/2020 08:03, Oleksandr Andrushchenko wrote:
>>>> diff --git a/xen/arch/arm/pci/pci-access.c b/xen/arch/arm/pci/pci-access.c
>>>> new file mode 100644
>>>> index 0000000000..c53ef58336
>>>> --- /dev/null
>>>> +++ b/xen/arch/arm/pci/pci-access.c
>>>> @@ -0,0 +1,101 @@
>>>> +/*
>>>> + * Copyright (C) 2020 Arm Ltd.
>> I think SPDX will fit better in any new code.
> 
> While I would love to use SPDX in Xen, there was some push back in the past to use it. So the new code should use the full-blown copyright until there is an agreement to use it.

Ack. We will use the copyright until we will get the confirmation from the community to use the SPDX in XEN.
> 
>>> 
>>>> +    list_add_tail(&bridge->node, &pci_host_bridges);
>>> It looks like &pci_host_bridges should be an ordered list, ordered by
>>> segment number?
>> Why? Do you expect bridge access in some specific order so ordered
>> list will make it faster?
> 
> Access to the configure space will be pretty random. So I don't think ordering the list will make anything better.
> 
> However, looking up for the bridge for every config spec access is pretty slow. When I was working on the PCI passthrough, I wanted to look whether it would be possible to have a pointer to the PCI host bridge passed in argument to the helpers (rather than the segment).

Yes true every config space access has to scan the host-bridges list to find the corresponding host-bridge. I will try to find better solution so that no need to scan the host-bridge every time for read/write access.


> Cheers,
> 
> -- 
> Julien Grall