linux-kernel - Re: [PATCH soc] ARM: use ARM_SINGLE

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Date:	Fri, 22 May 2015 18:28:16 +0200
From:	Stefan Agner <stefan@...er.ch>
To:	Daniel Thompson <daniel.thompson@...aro.org>
Cc:	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>, manabian@...il.com,
	linux-kernel@...r.kernel.org,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	olof@...om.net
Subject: Re: [PATCH soc] ARM: use ARM_SINGLE_ARMV7M for ARMv7-M platforms

On 2015-05-22 17:56, Daniel Thompson wrote:
> On 22/05/15 16:29, Maxime Coquelin wrote:
>> 2015-05-22 16:50 GMT+02:00 Arnd Bergmann <arnd@...db.de>:
>>> [one small request as I have four armv7-m folks on Cc already:
>>>   could one of you try to fix the warning that I get with every
>>>   single build: "/git/arm-soc/arch/arm/kernel/head-nommu.S: Assembler
>>> messages: /git/arm-soc/arch/arm/kernel/head-nommu.S:167: Warning:
>>> Use of r13 as a source register is deprecated when r15 is the
>>> destination register."]
>>
>> Moving r13 to r12 and returning r12 seems to do the job (see below).
>> But I don't know if there is a more elegant way, and if it is also
>> valid for other architectures than armv7-m.
> 
> Why not just s/r13/r11/?
> 
> (works for me but I'm only working on single core system)

For ARMv7-M this works, since r11 is not used in the processors
PROCINFO_INITFUNC function (__cpu_flush in struct proc_info_list, which
is __v7m_setup in proc-v7m.S).

However, afaik, head-nommu.S can be used by different processors too,
hence that register needs to be free to use for all possible __cpu_flush
implementations.

That said, proc-v7.S stores r11 on the stack, so it really seems that
r11 is ok to use?

--
Stefan


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