From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752627AbbIHD4k (ORCPT ); Mon, 7 Sep 2015 23:56:40 -0400 Received: from ozlabs.org ([103.22.144.67]:42645 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751590AbbIHD4i (ORCPT ); Mon, 7 Sep 2015 23:56:38 -0400 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" X-Mailer: Evolution 3.12.11-0ubuntu3 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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