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Re: [Xen-devel] [PATCH v4 2/2] IB/qib: use arch_phys_wc_add()
- To: Doug Ledford <dledford@xxxxxxxxxx>
- From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>
- Date: Wed, 22 Apr 2015 17:33:48 +0200
- Cc: linux-fbdev@xxxxxxxxxxxxxxx, mst@xxxxxxxxxx, Daniel Vetter <daniel.vetter@xxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, jbeulich@xxxxxxxx, sean.hefty@xxxxxxxxx, cocci@xxxxxxxxxxxxxxx, ville.syrjala@xxxxxxxxxxxxxxx, roland@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, Arnd Bergmann <arnd@xxxxxxxx>, Rickard Strandqvist <rickard_strandqvist@xxxxxxxxxxxxxxxxxx>, linux-rdma@xxxxxxxxxxxxxxx, Roland Dreier <roland@xxxxxxxxxxxxxxx>, Tomi Valkeinen <tomi.valkeinen@xxxxxx>, Suresh Siddha <sbsiddha@xxxxxxxxx>, Dave Airlie <airlied@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Jean-Christophe Plagniol-Villard <plagnioj@xxxxxxxxxxxx>, hal.rosenstock@xxxxxxxxx, Antonino Daplas <adaplas@xxxxxxxxx>, Stefan Bader <stefan.bader@xxxxxxxxxxxxx>, infinipath@xxxxxxxxx, Bjorn Helgaas <bhelgaas@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Mike Marciniszyn <mike.marciniszyn@xxxxxxxxx>, Toshi Kani <toshi.kani@xxxxxx>, "Luis R. Rodriguez" <mcgrof@xxxxxxxxxxxxxxxx>, Dennis Dalessandro <dennis.dalessandro@xxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, luto@xxxxxxxxxxxxxx, david.vrabel@xxxxxxxxxx, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 22 Apr 2015 15:33:57 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
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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