linux-kernel - Re: [PATCH] drm/i915: check to see if SIMD registers are available before using SIMD

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Date:   Sun, 03 May 2020 21:20:19 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Christoph Hellwig <hch@...radead.org>
Cc:     linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, bigeasy@...utronix.de,
        tglx@...utronix.de, stable@...r.kernel.org
Subject: Re: [PATCH] drm/i915: check to see if SIMD registers are available before using SIMD

Quoting Christoph Hellwig (2020-05-01 19:07:31)
> 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?

What is this core functionality that provides movntqda?
-Chris