Re: [PATCH] powerpc32: memcpy: only use dcbz once cache is enabled

[Michael Ellerman <mpe@ellerman.id.au>]

On Mon, 2015-09-07 at 16:24 +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, the 'dcbz'
> instruction is replaced by 'dcbt' which is harmless if cache is not
> enabled, and which helps a bit (allthough not as much as dcbz) if
> cache is already enabled.
> 
> Once the initial MMU is setup, in machine_init() we patch memcpy()
> by replacing the temporary 'dcbt' by 'dcbz'
> 
> Reported-by: Michal Sojka <sojkam1@fel.cvut.cz>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>


Is there some reason you can't use the normal cpu feature sections? See
arch/powerpc/lib/memcpy_64.S for an example of what I mean.

cheers