linux-kernel - Re: [PATCH] IB/ipath: use arch_phys_wc

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Date:	Mon, 27 Apr 2015 09:46:21 -0700
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Doug Ledford <dledford@...hat.com>,
	Mike Marciniszyn <infinipath@...el.com>, roland@...nel.org,
	"Hefty, Sean" <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	linux-rdma@...r.kernel.org
Cc:	Andy Lutomirski <luto@...capital.net>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>,
	Mike Marciniszyn <mike.marciniszyn@...el.com>,
	Roland Dreier <roland@...estorage.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Juergen Gross <jgross@...e.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Dave Airlie <airlied@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Antonino Daplas <adaplas@...il.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Ville Syrjälä <syrjala@....fi>,
	Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
	Borislav Petkov <bp@...e.de>, Davidlohr Bueso <dbueso@...e.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Arnd Bergmann <arnd@...db.de>,
	Stefan Bader <stefan.bader@...onical.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Jan Beulich <jbeulich@...e.com>,
	Toshi Kani <toshi.kani@...com>,
	Roger Pau Monné <roger.pau@...rix.com>,
	linux-fbdev <linux-fbdev@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH] IB/ipath: use arch_phys_wc_add() and require PAT disabled

On Wed, Apr 22, 2015 at 12:26 PM, Luis R. Rodriguez
<mcgrof@...not-panic.com> wrote:
> From: "Luis R. Rodriguez" <mcgrof@...e.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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