linux-kernel - Re: [PATCH 01/24] PCI: Add iobusn

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Date:	Fri, 10 Feb 2012 15:40:53 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Tony Luck <tony.luck@...el.com>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 01/24] PCI: Add iobusn_resource

On Fri, Feb 10, 2012 at 12:51 PM, Jesse Barnes <jbarnes@...tuousgeek.org> wrote:
> On Mon, 6 Feb 2012 10:55:14 -0800
> Yinghai Lu <yinghai@...nel.org> wrote:
>
>> On Mon, Feb 6, 2012 at 10:48 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>> >> +struct resource iobusn_resource = {
>> >> +       .name   = "PCI busn",
>> >> +       .start  = 0,
>> >> +       .end    = 0xffffff,
>> >> +       .flags  = IORESOURCE_BUS,
>> >> +};
>> >
>> > I'm not sure this should be global.  iomem_resource and
>> > ioport_resource *are* really global, because they refer to processor
>> > address space that is the same for everybody.  But PCI bus numbers are
>> > specific to PCI.  Some machines don't have PCI at all, and there are
>> > different bus architectures to which this doesn't apply.
>>
>> that does not hurt them.
>
> Yes but it's superfluous and confusing if you're porting to a new arch
> or looking at changes in generic code that may affect you.
>
>> > The 0-0xffffff range is misleading because it includes both the domain
>> > and the bus number, and it's meaningless to allocate ranges that cross
>> > domain boundaries.  For example, [bus 0x0000f0-0x000120] includes bus
>> > numbers from domain 0000 and domain 0001, which doesn't make any sense
>> > because a bus can only be in one domain.
>>
>> allocation code will make sure it will be cross the boundary for domain.
>
> But that means everyone reading it will do a double take, have to dig
> into the implementation, and only then say "ah yeah ok it looks
> correct" rather than it being obvious from the fact that the resource
> is tracked on a per-domain basis.
>
>> > I think it would make more sense to keep this bus number resource in a
>> > per-host bridge structure.  Then we wouldn't need to include the
>> > domain number at all because the host bridge determines the domain.
>>
>> not sure. insert the all busn_res of all peer root buses into one
>> global iobusn_resource
>> looks more simple.
>
> In what sense?  Simpler in the sense of your current implementation,
> but not simpler at all to someone just reading the code...

ok, will check if i could drop iobusn_resource.

Yinghai
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