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From: John Baldwin <jhb@freebsd.org>
To: freebsd-current@freebsd.org
Subject: Re: [PATCH] PCI bus number management
Date: Fri, 7 Feb 2014 15:27:41 -0500
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 (bigwig.baldwin.cx); Fri, 07 Feb 2014 15:47:34 -0500 (EST)
Cc: Julian Stecklina <jsteckli@os.inf.tu-dresden.de>
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On Friday, February 07, 2014 7:43:51 am Julian Stecklina wrote:
> On 02/06/2014 08:37 PM, John Baldwin wrote:
> > I would like to commit this to HEAD soon but thought I would post it for some 
> > pre-commit testing for the brave. :)  If you are really brave, try booting 
> > with 'hw.pci.clear_buses=1' which will force the kernel to renumber all buses 
> > in the system.
> 
> This is a really bad idea, because BIOS/SMM tends to have those
> hardcoded. Or am I misunderstanding the purpose of this patch?

The BIOS just programs them initially.  By default we use whatever the BIOS
programs and only rely on this infrastructure if we need to grow the tree
for some reason (e.g. hotplug).  However, it is definitely valid for an OS
to reassign bus numbers as it sees fit.

-- 
John Baldwin