linux-kernel - Re: [PATCH 02/11] PCI: Try to allocate mem64 above 4G at first

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Message-ID: <4FC5CEF1.6000509@snewbury.org.uk>
Date:	Wed, 30 May 2012 08:40:33 +0100
From:	Steven Newbury <steve@...wbury.org.uk>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Yinghai Lu <yinghai@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/11] PCI: Try to allocate mem64 above 4G at first

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On 30/05/12 00:27, Bjorn Helgaas wrote:
> On Tue, May 29, 2012 at 2:40 PM, Yinghai Lu <yinghai@...nel.org>
> wrote:
>> On Tue, May 29, 2012 at 12:23 PM, Bjorn Helgaas
>> <bhelgaas@...gle.com> wrote:
>>> On Tue, May 29, 2012 at 12:17 PM, Yinghai Lu
>>> <yinghai@...nel.org> wrote:
>>>> On Tue, May 29, 2012 at 10:57 AM, H. Peter Anvin
>>>> <hpa@...or.com> wrote:
>>>>> On 05/29/2012 10:55 AM, Yinghai Lu wrote:

*SNIP*

>> 
>> 
>> ok, please check the version, that put back PCI_MAX_RESOURCE_32
>> for io ports.
>> 
>> also RFC to limit for 16 bit ioport handling.  only help other
>> arches that does support 32bit ioports but have bridges only
>> support 16bit io ports.
> 
> I don't understand this one at all.  It looks like you mashed
> together at least two changes: (1) prefer I/O space above 64K if
> available, and (2) mark secondary bus resources with
> IORESOURCE_IO_32 when the P2P bridge I/O window address decode type
> is PCI_IO_RANGE_TYPE_32 and use that to limit allocations.
> 
> I don't see the justification for (1).  What problem does this
> solve?
> 
I can potentially see this helping with hotplug, where a new device
has only 16 bit io ports, but if there's no space remaining under 64k
allocation would fail.  Preferring above 64k means preserving that
limited resource.  This is exactly equivalent to my original
motivation for preferring 64 bit PCI mem in order to preserve 32 bit
address space for hotplug devices without 64 bit BARs.
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