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

[Julien Grall <julien@xxxxxxx>]

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.
> > > +    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).
Cheers,

--
Julien Grall