linux-kernel - Re: [PATCH RFC] ARM: vexpress: Use assembler mnemonic for WFI in platform_do

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Message-ID: <CAHkRjk6Fq+1b_uM+DFACS1QVd7B6_1XhqRw-27i88U1VyvLk+Q@mail.gmail.com>
Date:	Mon, 22 Aug 2011 10:43:26 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Jamie Iles <jamie@...ieiles.com>
Cc:	Nick Bowler <nbowler@...iptictech.com>,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RFC] ARM: vexpress: Use assembler mnemonic for WFI in platform_do_lowpower.

On 19 August 2011 22:14, Jamie Iles <jamie@...ieiles.com> wrote:
> On Fri, Aug 19, 2011 at 03:26:38PM -0400, Nick Bowler wrote:
>> On 2011-08-19 19:15 +0100, Jamie Iles wrote:
>> > On Fri, Aug 19, 2011 at 02:03:24PM -0400, Nick Bowler wrote:
>> [...]
>> > > -         /*
>> > > -          * here's the WFI
>> > > -          */
>> > > -         asm(".word      0xe320f003\n"
>> > > +         asm("wfi\n"
>> > >               :
>> > >               :
>> > >               : "memory", "cc");
>> >
>> > There's a wfi() macro defined in arch/arm/include/asm/system.h that
>> > could be used here.
>>
>> Indeed, thanks for pointing that out.
>>
>> I'm a little wary, however: the wfi macro does not include the "cc"
>> clobber that this code has currently, and I don't know what the
>> implications of removing it are.  There appears to be no current
>> users of the wfi macro.
>
> As far as I can tell from the ARM ARM, the instruction shouldn't alter
> the condition flags so the cc clobber shouldn't be necessary.

I also don't see why we need the 'cc' flag in here. Just use the wfi() macro.

-- 
Catalin
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