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Date:   Wed, 28 Jun 2017 10:34:11 +0200
From:   Ralf Baechle <ralf@linux-mips.org>
To:     "Maciej W. Rozycki" <macro@imgtec.com>
Cc:     Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>,
        Matt Redfearn <Matt.Redfearn@imgtec.com>,
        Aleksandar Markovic <aleksandar.markovic@rt-rk.com>,
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        Miodrag Dinic <Miodrag.Dinic@imgtec.com>,
        Goran Ferenc <Goran.Ferenc@imgtec.com>
Subject: Re: [PATCH 3/8] MIPS: R6: Fix PREF instruction usage by memcpy for
 MIPS R6
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On Wed, Jun 28, 2017 at 03:36:54AM +0100, Maciej W. Rozycki wrote:

> On Wed, 28 Jun 2017, Leonid Yegoshin wrote:
> 
> > The bigger problem is a prefetch overrun to device registers. AT use is just
> > nuisance.
> 
>  That isn't however what the patch addresses, not at least according to 
> the description provided.
> 
>  How far beyond the data copied do we prefetch anyway, and can't we simply 
> waste a page's worth of space or so at the physical end of each RAM area 
> present in a given system?  Or perhaps use it for something we know for 
> sure that won't ever be copied.

Prefetching may also bring data which has just been flushed back into
caches so until this is fixed properly it's not a good idea on non-coherent
platforms.

  Ralf