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

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Message-ID: <4FC64B3E.2020002@zytor.com>
Date:	Wed, 30 May 2012 09:30:54 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Steven Newbury <steve@...wbury.org.uk>,
	Yinghai Lu <yinghai@...nel.org>,
	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

On 05/30/2012 09:27 AM, Bjorn Helgaas wrote:
> 
> You're right, the spec does allow the upper 16 bits of I/O BARs to be
> hardwired to zero (PCI spec rev 3.0, p. 226), so this part does make
> some sense.  I don't think it applies to x86, since I don't think
> there's a way to generate an I/O access to anything above 64K, but it
> could help other arches.
> 
> I'm inclined to be conservative and wait until we find a problem where
> a patch like this would help.
> 

The really conservative thing is to just use 16-bit addresses for I/O on
all platforms.  I think a lot of non-x86 platforms does that.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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