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Subject: Re: [PATCH v3] powerpc32: memcpy: only use dcbz once cache is enabled
From: Scott Wood <scottwood@freescale.com>
To: Christophe Leroy <christophe.leroy@c-s.fr>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras
 <paulus@samba.org>, Michael Ellerman <mpe@ellerman.id.au>,
 <sojkam1@fel.cvut.cz>, <linux-kernel@vger.kernel.org>,
 <linuxppc-dev@lists.ozlabs.org>
Date: Fri, 11 Sep 2015 16:35:15 -0500
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On Fri, 2015-09-11 at 16:33 +0200, Christophe Leroy wrote:
> memcpy() uses instruction dcbz to speed up copy by not wasting time
> loading cache line with data that will be overwritten.
> Some platform like mpc52xx do no have cache active at startup and
> can therefore not use memcpy(). Allthough no part of the code
> explicitly uses memcpy(), GCC makes calls to it.
> 
> This patch modifies memcpy() such that at startup, memcpy()
> unconditionally jumps to generic_memcpy() which doesn't use
> the dcbz instruction.
> 
> Once the initial MMU is set up, in machine_init() we patch memcpy()
> by replacing this inconditional jump by a NOP
> 
> Reported-by: Michal Sojka <sojkam1@fel.cvut.cz>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
> changes in v2:
>   Using feature-fixups instead of hardcoded call to patch_instruction()
>   Handling of memset() added
> changes in v3:
>   Not using anymore feature-fixups
>   Handling of memset() removed

Why was handling of memset() removed?

-Scott