Re: [PATCH] IB/ipath: use arch_phys_wc_add() and require PAT disabled

From: Luis R. Rodriguez
Date: Mon Apr 27 2015 - 12:46:48 EST

On Wed, Apr 22, 2015 at 12:26 PM, Luis R. Rodriguez
<mcgrof@xxxxxxxxxxxxxxxx> wrote:
> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>
> 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 ?

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