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

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Date:   Fri, 1 May 2020 11:07:31 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, bigeasy@...utronix.de,
        tglx@...utronix.de, chris@...is-wilson.co.uk,
        stable@...r.kernel.org
Subject: Re: [PATCH] drm/i915: check to see if SIMD registers are available
 before using SIMD

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?