Date: Wed, 7 Jan 2004 16:34:49 -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: <20040108003449.GA7586@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> <20040107235633.GA7312@sgi.com>
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From: jbarnes@sgi.com (Jesse Barnes)
Sender: linux-kernel-owner@vger.kernel.org
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On Wed, Jan 07, 2004 at 03:56:33PM -0800, Jesse Barnes wrote:
> 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.

This is also the easiest solution to implement for the sn2 platform.
Honestly, I haven't used any PCI-X chipsets (nor do I know of any) that
exploit this new relaxed ordering feature, so I'm only guessing at how
it might be usefully exported to the driver API.

The sn2 platform actually _always_ behaves as though relaxed ordering
were enabled, so all we really need to implement this correctly is a
read_relaxed(), which will be a read() but without the software
workaround we put in place to conform to the PCI PIO/DMA semantics.

Maybe we can just add read_relaxed() for now and deal with other
chipsets that allow relaxed ordering as they appear?

Thanks,
Jesse
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