Date: Wed, 7 Jan 2004 15:56:33 -0800
To: Greg KH <greg@kroah.com>
Cc: Grant Grundler <grundler@parisc-linux.org>,
       Matthew Wilcox <willy@debian.org>, linux-pci@atrey.karlin.mff.cuni.cz,
       linux-kernel@vger.kernel.org, jeremy@sgi.com
Subject: Re: [RFC] Relaxed PIO read vs. DMA write ordering
Message-ID: <20040107235633.GA7312@sgi.com>
Mail-Followup-To: Greg KH <greg@kroah.com>,
	Grant Grundler <grundler@parisc-linux.org>,
	Matthew Wilcox <willy@debian.org>,
	linux-pci@atrey.karlin.mff.cuni.cz, linux-kernel@vger.kernel.org,
	jeremy@sgi.com
References: <20040107175801.GA4642@sgi.com> <20040107190206.GK17182@parcelfarce.linux.theplanet.co.uk> <20040107222142.GB14951@colo.lackof.org> <20040107230712.GB6837@sgi.com> <20040107232754.GA2807@kroah.com>
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From: jbarnes@sgi.com (Jesse Barnes)
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On Wed, Jan 07, 2004 at 03:27:54PM -0800, Greg KH wrote:
> On Wed, Jan 07, 2004 at 03:07:12PM -0800, Jesse Barnes wrote:
> > 
> >   1) add pcix_enable_relaxed() and read_relaxed() (read() would always be
> >      ordered)
> 
> This probably preserves the current situation best, enabling driver
> writers to be explicit in knowing what is happening.

That's what I figured too.  It also seems like it has the lowest
probability of introducing PIO vs. DMA races, since you have to
explicitly change a read() call.

What about compatibility though?  How should the interface behave if
it's accessing a PCI-X device that happens to be in PCI mode?  Ideally,
we could add these calls in and introduce no penalty for platforms that
don't support it...

Thanks,
Jesse
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