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Message-ID: <49EBD934.4070909@gmail.com>
Date: Sun, 19 Apr 2009 20:08:52 -0600
From: Robert Hancock <hancockrwd@gmail.com>
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To: Roland Dreier <rdreier@cisco.com>
CC: Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       "Robert P. J. Day" <rpjday@crashcourse.ca>,
       Hitoshi Mitake <h.mitake@gmail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: arch/x86/Kconfig selects invalid HAVE_READQ, HAVE_WRITEQ vars
References: <alpine.LFD.2.00.0904191543530.11789@localhost.localdomain>	<adaab6c1h7c.fsf@cisco.com> <20090419214602.GA21527@elte.hu>	<49EB9F59.4080904@zytor.com> <20090419223519.GA27706@elte.hu> <adaskk4ywf9.fsf@cisco.com>
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Roland Dreier wrote:
>  > Also, atomicity might not be possible to guarantee on the bus level: 
>  > say the device sits on a 32-bit PCI bus. (No matter what instruction 
>  > the CPU gets, a readq/writeq there has to be done as two 32-bit bus 
>  > accesses.)
> 
> Well, the conventional PCI devices I know of with 64-bit registers were
> PCI-X cards, keyed so they would only fit into a 64-bit slot.  And of
> course there is no such thing as 32-bit PCI Express.

It's quite possible to use most 64-bit PCI-X cards in a 32-bit slot, 
with the 64-bit part of the card not plugged into anything. It's 
supposed to work (as long as the card can handle the voltage the slot uses).