From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Luis R. Rodriguez" <mcgrof@suse.com>
Date: Wed, 22 Apr 2015 15:33:48 +0000
Subject: Re: [PATCH v4 2/2] IB/qib: use arch_phys_wc_add()
Message-Id: <20150422153348.GD5622@wotan.suse.de>
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To: Doug Ledford <dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: "Luis R. Rodriguez" <mcgrof-3uybbJdB1yH774rrrx3eTA@public.gmane.org>, infinipath-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, sean.hefty-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, hal.rosenstock-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org, mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cocci-/FJkirnvOdkvYVN+rsErww@public.gmane.org, Toshi Kani <toshi.kani-VXdhtT5mjnY@public.gmane.org>, Rickard Strandqvist <rickard_strandqvist-IW2WV5XWFqGZkjO+N0TKoMugMpMbD5Xr@public.gmane.org>, Mike Marciniszyn <mike.marciniszyn-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Roland Dreier <roland-BHEL68pLQRGGvPXPguhicg@public.gmane.org>, Dennis Dalessandro <dennis.dalessandro-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Suresh Siddha <sbsiddha-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, Juergen Gross <jgross-IBi9RG/b67k@public.gmane.org>, Daniel Vetter <daniel.vetter-/w4YWyX8dFk@public.gmane.org>, Dave Airlie <airlied-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Bjorn Helgaas <bhelgaas-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Antonino Daplas <adaplas-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Jean-Christophe Plagniol-Villard <plagnioj-sclMFOaUSTBWk0Htik3J/w@public.gmane.org>, Tomi Valkeinen <tomi.valkeinen-l0cyMroinI0@public.gmane.org>Dave

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