From: Shawn Guo <shawn.guo@freescale.com>
Subject: Re: [PATCH] ARM: convert all "mov.* pc, reg" to "bx reg" for ARMv6+
Date: Wed, 2 Jul 2014 13:10:27 +0800
Message-ID: <20140702051026.GD16176@dragon>
References: <E1X20Rs-00082S-KI@rmk-PC.arm.linux.org.uk>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Cc: Andrew Lunn <andrew@lunn.ch>, kvm@vger.kernel.org, linux-sh@vger.kernel.org,
 Kevin Hilman <khilman@deeprootsystems.com>, Sekhar Nori <nsekhar@ti.com>,
 linux-tegra@vger.kernel.org, Thierry Reding <thierry.reding@gmail.com>,
 kvmarm@lists.cs.columbia.edu, linux-samsung-soc@vger.kernel.org,
 Kukjin Kim <kgene.kim@samsung.com>, Herbert Xu <herbert@gondor.apana.org.au>,
 Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
 Magnus Damm <magnus.damm@gmail.com>, Gleb Natapov <gleb@kernel.org>,
 Tony Lindgren <tony@atomide.com>, xen-devel@lists.xenproject.org,
 Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>,
 Jason Cooper <jason@lakedaemon.net>, Stephen Warren <swarren@wwwdotorg.org>,
 Marc Zyngier <marc.zyngier@arm.com>,
 Hans Ulli Kroll <ulli.kroll@googlemail.com>,
 Haojian Zhuang <haojian.zhuang@gmail.com>, Simon Horman <horms@verge.net.au>,
 Ben Dooks <ben-linux@fluff.org>,
To: Russell King <rmk+kernel@arm.linux.org.uk>
Content-Disposition: inline
In-Reply-To: <E1X20Rs-00082S-KI@rmk-PC.arm.linux.org.uk>
Sender: "linux-arm-kernel" <linux-arm-kernel-bounces@lists.infradead.org>
Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org

On Tue, Jul 01, 2014 at 04:58:24PM +0100, Russell King wrote:
> ARMv6 and greater introduced a new instruction ("bx") which can be used
> to return from function calls.  Recent CPUs perform better when the
> "bx lr" instruction is used rather than the "mov pc, lr" instruction,
> and this sequence is strongly recommended to be used by the ARM
> architecture manual (section A.4.1.1).
> 
> We provide a new macro "ret" with all its variants for the condition
> code which will resolve to the appropriate instruction.
> 
> Rather than doing this piecemeal, and miss some instances, change all
> the "mov pc" instances to use the new macro, with the exception of
> the "movs" instruction and the kprobes code.  This allows us to detect
> the "mov pc, lr" case and fix it up - and also gives us the possibility
> of deploying this for other registers depending on the CPU selection.
> 
> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> ---
...
>  arch/arm/mach-imx/suspend-imx6.S         |  5 ++--

Tested-by: Shawn Guo <shawn.guo@freescale.com>