From: Sekhar Nori <nsekhar-l0cyMroinI0@public.gmane.org>
Subject: Re: [PATCH] ARM: convert all "mov.* pc, reg" to "bx reg" for ARMv6+
Date: Wed, 2 Jul 2014 17:01:04 +0530
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Cc: Andrew Lunn <andrew-g2DYL2Zd6BY@public.gmane.org>, <kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
        <linux-sh-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Kevin Hilman <khilman-1D3HCaltpLuhEniVeURVKkEOCMrvLtNR@public.gmane.org>,
        <linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
        Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
        <kvmarm-FPEHb7Xf0XXUo1n7N8X6UoWGPAHP3yOg@public.gmane.org>, <linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
        Kukjin
 Kim <kgene.kim-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>,
        Herbert Xu <herbert-lOAM2aK0SrRLBo1qDEOMRrpzq4S04n8Q@public.gmane.org>,
        Stefano Stabellini <stefano.stabellini-mvvWK6WmYclDPfheJLI6IQ@public.gmane.org>,
        Magnus Damm
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        Tony Lindgren
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        Hans Ulli Kroll <ulli.kroll-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org>,
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	<h
To: Russell King <rmk+kernel-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>,
        <linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
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On Tuesday 01 July 2014 09:28 PM, 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-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>

> ---

>  arch/arm/mach-davinci/sleep.S            |  2 +-

I build, boot and suspend-to-RAM tested on DA850 which should exercise
the path you modified. DaVinci devices are ARMv5 (ARM926) so the new bx
instruction does not really get used.

Acked-by: Sekhar Nori <nsekhar-l0cyMroinI0@public.gmane.org>

Thanks,
Sekhar