linux-kernel - Re: [PATCH v2] PCI: Always set prefetchable base/limit upper32 registers

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Date:	Tue, 01 Dec 2009 13:14:08 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Grant Grundler <grundler@...isc-linux.org>
CC:	Alex Williamson <alex.williamson@...com>, jbarnes@...tuousgeek.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: Always set prefetchable base/limit upper32	registers

Grant Grundler wrote:
> On Tue, Dec 01, 2009 at 12:40:03PM -0800, Yinghai Lu wrote:
> ...
>>> I assumed Yinghai's objection was based on a specific problem he had
>>> seen with writing upper32 register. Bjorn asked the right question.
>>> If there isn't a specific problem, I'd prefer AW's simpler patch.
>> we just should not touch that register if the HW only support 32bit pref mmio.
> 
> Why not?
> 
> I agree the PCI-PCI spec defines how to determine if a PCI Bridge supports
> 64-bit Pref MMIO (using upper32 - or not). But spec also doesn't prohibit
> writing to a read-only register.  Writing this Read-Only register so far
> hasn't caused any problems.

if we can find out that is 32bit mmio pref, why waste cycle to write value to them?

YH
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