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

  • To: Julien Grall <julien@xxxxxxx>
  • From: Rahul Singh <Rahul.Singh@xxxxxxx>
  • Date: Mon, 27 Jul 2020 15:27:21 +0000
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  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>, "andrew.cooper3@xxxxxxxxxx" <andrew.cooper3@xxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, "jbeulich@xxxxxxxx" <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, nd <nd@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, "roger.pau@xxxxxxxxxx" <roger.pau@xxxxxxxxxx>
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  • Thread-topic: [RFC PATCH v1 1/4] arm/pci: PCI setup and PCI host bridge discovery within XEN on ARM.

> On 24 Jul 2020, at 9:05 am, Julien Grall <julien@xxxxxxx> 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



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