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


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).


Julien Grall



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