Date: Wed, 22 Apr 2015 17:33:48 +0200
From: "Luis R. Rodriguez" <mcgrof@suse.com>
To: Doug Ledford <dledford@redhat.com>
Cc: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>, infinipath@intel.com,
        roland@kernel.org, sean.hefty@intel.com, hal.rosenstock@gmail.com,
        linux-rdma@vger.kernel.org, luto@amacapital.net, mst@redhat.com,
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        Toshi Kani <toshi.kani@hp.com>,
        Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>,
        Mike Marciniszyn <mike.marciniszyn@intel.com>,
        Roland Dreier <roland@purestorage.com>,
        Dennis Dalessandro <dennis.dalessandro@intel.com>,
        Suresh Siddha <sbsiddha@gmail.com>, Ingo Molnar <mingo@elte.hu>,
        Thomas Gleixner <tglx@linutronix.de>, Juergen Gross <jgross@suse.com>,
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        Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>,
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        Stefan Bader <stefan.bader@canonical.com>, konrad.wilk@oracle.com,
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        Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>,
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Subject: Re: [PATCH v4 2/2] IB/qib: use arch_phys_wc_add()
Message-ID: <20150422153348.GD5622@wotan.suse.de>
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 <1429710878.45956.94.camel@redhat.com>
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On Wed, Apr 22, 2015 at 09:54:38AM -0400, Doug Ledford wrote:
> On Tue, 2015-04-21 at 14:50 -0700, Luis R. Rodriguez wrote:
> 
> This:
> > +	/* MTRR was used if this is non-zero */
> > +	if (!dd->wc_cookie)
> >  		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> 
> And this:
> > +		dd->wc_cookie = arch_phys_wc_add(pioaddr, piolen);
> > +		if (dd->wc_cookie < 0)
> > +			ret = -EINVAL;
> 
> don't agree on what wc_cookie will be on error.

Can you elaborate? The one below is the one that starts things,
and arch_phys_wc_add() will return 0 on PAT systems. For non-PAT
systems it will return a number > 0 *iff* a valid MTRR was added.
It will return negative onloy on error then.

The change above is meant to replace a check put in place to see
if PAT was enabled. The way we replace this is to ensure that
arch_phys_wc_add() returned 0.

If you disagree it'd be great if you can elaborate why.

  Luis
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