From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 1EEAC1A0163 for ; Tue, 8 Sep 2015 13:56:37 +1000 (AEST) Message-ID: <1441684596.14597.5.camel@ellerman.id.au> Subject: Re: [PATCH] powerpc32: memcpy: only use dcbz once cache is enabled From: Michael Ellerman To: Christophe Leroy Cc: Benjamin Herrenschmidt , Paul Mackerras , scottwood@freescale.com, sojkam1@fel.cvut.cz, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Date: Tue, 08 Sep 2015 13:56:36 +1000 In-Reply-To: <20150907142444.CA8F31A241A@localhost.localdomain> References: <20150907142444.CA8F31A241A@localhost.localdomain> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 > Signed-off-by: Christophe Leroy 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