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Date:   Fri, 1 May 2020 15:55:14 -0600
From:   "Jason A. Donenfeld" <>
To:     Christoph Hellwig <>
Cc:     LKML <>,,
        dri-devel <>,
        Sebastian Siewior <>,
        Thomas Gleixner <>,
        Chris Wilson <>,
        stable <>
Subject: Re: [PATCH] drm/i915: check to see if SIMD registers are available
 before using SIMD

On Fri, May 1, 2020 at 12:07 PM Christoph Hellwig <> wrote:
> On Thu, Apr 30, 2020 at 04:10:16PM -0600, Jason A. Donenfeld wrote:
> > Sometimes it's not okay to use SIMD registers, the conditions for which
> > have changed subtly from kernel release to kernel release. Usually the
> > pattern is to check for may_use_simd() and then fallback to using
> > something slower in the unlikely case SIMD registers aren't available.
> > So, this patch fixes up i915's accelerated memcpy routines to fallback
> > to boring memcpy if may_use_simd() is false.
> Err, why does i915 implements its own uncached memcpy instead of relying
> on core functionality to start with?

I was wondering the same. It sure does seem like this ought to be more
generalized functionality, with a name that represents the type of
transfer it's optimized for (wc or similar).

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