[edk2-devel] PciBus scan: Does it support scan from EndBusNum to StartBusNum?

[Pedro Falcato]

On Tue, Feb 21, 2023 at 3:08 AM Yoshinoya <yoshinoyatoko at 163.com> wrote:
>
> Hi
> Usually PciBus scan is from low bus num to high bus num.
>
> So, does it support scan from end bus num to start bus num?
>
> Thanks
Hi,

What do you mean? Why do you want this?

Do you want to number buses in reverse? That is technically doable
(apart from probably the host bridge itself) but absolutely useless.

If you mean "order of enumeration", then no. It is not possible. As
PCI(e) topology works, you always start at the host bridge(s)
(00:00.0) and its bus (bus 0, by definition), and then walk through
whatever bridges you find. You cannot really start at any other place,
unless you do some silly bruteforce method where you probe every bus
for a device; and that method would not allow you to configure the
buses and their BARs, as you need to.

-- 
Pedro


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