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From: "Pedro Falcato" <pedro.falcato@gmail.com>
To: devel@edk2.groups.io, yoshinoyatoko@163.com
Subject: Re: [edk2-devel] PciBus scan: Does it support scan from EndBusNum to StartBusNum?
Date: Tue, 21 Feb 2023 19:18:07 +0000	[thread overview]
Message-ID: <CAKbZUD2opZK-h+TSx4+sBCdc91fgA+r3DYn8XNBag5KYdxt7tQ@mail.gmail.com> (raw)
In-Reply-To: <2ee1fd81.20a.1866204f2cb.Coremail.yoshinoyatoko@163.com>

On Tue, Feb 21, 2023 at 3:08 AM Yoshinoya <yoshinoyatoko@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

  parent reply	other threads:[~2023-02-21 19:18 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-05 11:32 [edk2-devel] Python368.efi failed to run in shell environment Yoshinoya
2022-10-05 16:28 ` Michael D Kinney
2022-10-11 10:20   ` Yoshinoya
2022-10-18  9:04     ` Jayaprakash, N
2022-10-19  8:30       ` Yoshinoya
2022-10-19 13:16         ` Jayaprakash, N
2022-10-20  3:06           ` Yoshinoya
2022-10-20  3:18             ` Jayaprakash, N
2022-11-08  3:16 ` [edk2-devel] Access 64bit address space in 32bit mode Yoshinoya
2022-11-09 17:20   ` Andrew Fish
2022-11-09 18:58     ` vincent zimmer
2022-11-09 20:14       ` Andrew Fish
2023-02-18  0:55         ` [edk2-devel] PciBus scan: Does it support scan from EndBusNum to StartBusNum? Yoshinoya
2023-02-20  4:28           ` Yoshinoya
2023-02-21  1:27           ` Yoshinoya
2023-02-21  2:47             ` Yoshinoya
2023-02-21 19:18           ` Pedro Falcato [this message]
2023-02-22  1:10             ` Tiger Liu(BJ-RD)
2023-02-22  1:22               ` Pedro Falcato
2023-05-23  9:55           ` [edk2-devel] PciHostBridge: dynamic pcie bus limit assignment Yoshinoya
2022-11-09 20:40     ` [edk2-devel] Access 64bit address space in 32bit mode Brian J. Johnson
2023-01-03  9:04       ` [edk2-devel] PciBus driver: support pcie 4.0 bus/device enumeration ? Yoshinoya

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