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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Sun, 3 May 2020 14:35:03 -0600
Message-ID: <CAHmME9o51exzeeV6C95-9b=608-qFWag2X_jPTYEmuBUtUU3WQ@mail.gmail.com>
Subject: Re: [PATCH] drm/i915: check to see if SIMD registers are available
 before using SIMD
To:     Chris Wilson <chris@chris-wilson.co.uk>
Cc:     Sebastian Siewior <bigeasy@linutronix.de>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        intel-gfx@lists.freedesktop.org,
        LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        stable <stable@vger.kernel.org>
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On Sun, May 3, 2020 at 2:30 PM Chris Wilson <chris@chris-wilson.co.uk> wrote:
>
> Quoting Jason A. Donenfeld (2020-04-30 23:10:16)
> > 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.
> >
> > Cc: stable@vger.kernel.org
>
> The same argument as on the previous submission is that we return to the
> caller if we can't use movntqda as their fallback path should be faster
> than uncached memcpy.

Oh, THAT's what you meant before. Okay, will follow up.