linux-kernel - Re: [PATCH 23/23] x86, PCI: add pcibios_root

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Message-ID: <CAErSpo5T8-hrtMufDeo_EfupQX3neyoA9ufjN2UYro7-2SXc+Q@mail.gmail.com>
Date:	Wed, 7 Mar 2012 16:32:31 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Bjorn Helgaas <bjorn.helgaas@...il.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>, x86 <x86@...nel.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 23/23] x86, PCI: add pcibios_root_rescan

On Tue, Mar 6, 2012 at 11:29 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Tue, Mar 6, 2012 at 7:49 PM, Bjorn Helgaas <bjorn.helgaas@...il.com> wrote:
>
>>> my sandbridge system has cpu bus 0x7f, and 0xff in DSDT.
>>>
>>> but nehalem and westmere system does not have cpu bus 0xf8, ... 0xff.
>>
>> I think you're saying that on some machines, the BIOS decided not to
>> expose host bridges leading to CPU devices, and you want to discover
>> those devices anyway.  (What's the reason you want to discover them?)
>
> current code for mmconf will set pcibios_last_bios according to mmconf
> bus range.
>
> so it legacy peer root bus fix up will discover those cpu buses.
>
> then if some one remove them through
> echo 1 > /sys/devices/pci0000:ff/pci_bus/0000:ff/remove
>
> then
>
> echo 1 > /sys/bus/pci/rescan_root
>
> will not recover those cpu buses without this patch.

What's the reason we need to discover those CPU devices in the first place?

I don't think the current policy of blindly probing for things should
be continued forever.
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