Message-ID: <4FC64B3E.2020002@zytor.com>
Date: Wed, 30 May 2012 09:30:54 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Bjorn Helgaas <bhelgaas@google.com>
CC: Steven Newbury <steve@snewbury.org.uk>, Yinghai Lu <yinghai@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 02/11] PCI: Try to allocate mem64 above 4G at first
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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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