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From: "Luis R. Rodriguez" <mcgrof@suse.com>
Date: Mon, 27 Apr 2015 09:46:21 -0700
Message-ID: <CAB=NE6UHnEuMHfFaXBNr4F=RcDcEC3z6rX8-B_10Sbpr7kHkiA@mail.gmail.com>
Subject: Re: [PATCH] IB/ipath: use arch_phys_wc_add() and require PAT disabled
To: Doug Ledford <dledford@redhat.com>,
        Mike Marciniszyn <infinipath@intel.com>, roland@kernel.org,
        "Hefty, Sean" <sean.hefty@intel.com>,
        Hal Rosenstock <hal.rosenstock@gmail.com>, linux-rdma@vger.kernel.org
Cc: Andy Lutomirski <luto@amacapital.net>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Luis R. Rodriguez" <mcgrof@suse.com>,
        Suresh Siddha <sbsiddha@gmail.com>,
        Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>,
        Mike Marciniszyn <mike.marciniszyn@intel.com>,
        Roland Dreier <roland@purestorage.com>, Ingo Molnar <mingo@elte.hu>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, Juergen Gross <jgross@suse.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Dave Airlie <airlied@redhat.com>, Bjorn Helgaas <bhelgaas@google.com>,
        Antonino Daplas <adaplas@gmail.com>,
        Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>,
        Tomi Valkeinen <tomi.valkeinen@ti.com>,
        =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <syrjala@sci.fi>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
        Borislav Petkov <bp@suse.de>, Davidlohr Bueso <dbueso@suse.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Stefan Bader <stefan.bader@canonical.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <ville.syrjala@linux.intel.com>,
        David Vrabel <david.vrabel@citrix.com>,
        Jan Beulich <jbeulich@suse.com>, Toshi Kani <toshi.kani@hp.com>,
        =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= <roger.pau@citrix.com>,
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On Wed, Apr 22, 2015 at 12:26 PM, Luis R. Rodriguez
<mcgrof@do-not-panic.com> wrote:
> From: "Luis R. Rodriguez" <mcgrof@suse.com>
>
> We are burrying direct access to MTRR code support on
> x86 in order to take advantage of PAT. In the future we
> also want to make the default behaviour of ioremap_nocache()
> to use strong UC, use of mtrr_add() on those systems
> would make write-combining void.
>
> In order to help both enable us to later make strong
> UC default and in order to phase out direct MTRR access
> code port the driver over to arch_phys_wc_add() and
> annotate that the device driver requires systems to
> boot with PAT disabled, with the nopat kernel parameter.
>
> This is a worthy compromise given that the ipath device
> driver powers the old HTX bus cards that only work in
> AMD systems, while the newer IB/qib device driver
> powers all PCI-e cards. The ipath device driver is
> obsolete, hardware hard to find and because of this
> this its a reasonable compromise to make to require
> users of ipath to boot with nopat.

Hey folks, I realize its being discussed whether or not to remove the
driver entirely from the kernel but in the meantime, is this a
reasonable compromise ?

 Luis
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