linux-kernel - Re: [PATCH] mips: add arch_trigger_all_cpu

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Message-ID: <20141022222936.GE12296@jhogan-linux.le.imgtec.org>
Date:	Wed, 22 Oct 2014 23:29:36 +0100
From:	James Hogan <james.hogan@...tec.com>
To:	John Crispin <blogic@...nwrt.org>
CC:	<eunb.song@...sung.com>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mips: add arch_trigger_all_cpu_backtrace() function

Hi John,

On Wed, Oct 22, 2014 at 09:11:39AM +0200, John Crispin wrote:
> On 22/10/2014 08:54, Eunbong Song wrote:
> >>> +void arch_trigger_all_cpu_backtrace(bool); +#define
> >>> arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace
> > 
> >> What is the purpose of this define ? is this maybe a leftover from
> >> some regex/cleanups ?
> > 
> > Hi John.
> > Actually, I just follow the same function of sparc architecture.
> > You can find this in arch/sparc/include/asm/irq_64.h as below
> > 
> > void arch_trigger_all_cpu_backtrace(bool);
> > #define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace
> > 
> > I guess this is used for conditional compile. 
> > See below.
> > include/linux/nmi.h
> > #ifdef arch_trigger_all_cpu_backtrace
> > static inline bool trigger_all_cpu_backtrace(void)
> > {
> >         arch_trigger_all_cpu_backtrace(true);
> > 
> >         return true;
> > }
> > static inline bool trigger_allbutself_cpu_backtrace(void)
> > {
> >         arch_trigger_all_cpu_backtrace(false);
> >         return true;
> > }
> > #else
> > static inline bool trigger_all_cpu_backtrace(void)
> > {
> >         return false;
> > }
> > static inline bool trigger_allbutself_cpu_backtrace(void)
> > {
> >         return false;
> > }
> > #endif
> > 
> > Thanks. 
> >> John
> > 
> 
> i don't see how this is required for conditional compiles. the code
> define a->a which is bogus i think.

It's a pretty common pattern in the asm headers, in order to allow
generic code to use the preprocessor to see whether it was defined or
not.

Cheers
James
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