linux-kernel - Re: [v4,1/2] powerpc32: memcpy: only use dcbz once cache is enabled

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Message-Id: <20150917051327.C91901401EF@ozlabs.org>
Date:	Thu, 17 Sep 2015 15:13:27 +1000 (AEST)
From:	Michael Ellerman <mpe@...erman.id.au>
To:	LEROY Christophe <christophe.leroy@....fr>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>, scottwood@...escale.com,
	sojkam1@....cvut.cz
Cc:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [v4,1/2] powerpc32: memcpy: only use dcbz once cache is enabled

On Wed, 2015-16-09 at 10:04:51 UTC, LEROY Christophe 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@....cvut.cz>
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/1cd03890ea64795e53f17a94

cheers
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