Re: [PATCH v2 2/2] ARM: at91: pm: switch to the PIE infrastructure

From	Alexander Stein <alexander.stein@systec-electronic.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 2/2] ARM: at91: pm: switch to the PIE infrastructure
Date	2016-06-29 10:40 +0200
Message-ID	<rPjcm-1RY-29@gated-at.bofh.it> (permalink)
References	<rP9Zn-4vU-5@gated-at.bofh.it> <rPhax-GR-7@gated-at.bofh.it> <rPizE-1pB-13@gated-at.bofh.it>
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On Wednesday 29 June 2016 09:57:14, Alexandre Belloni wrote:
> On 29/06/2016 at 08:12:21 +0200, Alexander Stein wrote :
> > > +#if defined(CONFIG_CPU_V7)
> > > +	dsb();
> > > +	wfi();
> > > +#else
> > > +	asm volatile ("mcr	p15, 0, %0, c7, c0, 4" \
> > > +		      : : "r" (0) : "memory");
> > > +#endif
> > 
> > Why not defining wfi() for __LINUX_ARM_ARCH__ < 7 as it is done for dsb()
> > and friends in arch/arm/include/asm/barrier.h? So you can get rid of that
> > #if completly.
> 
> Well, Russell said it was not useful because "there's no architected WFI
> instruction which doesn't have CPU specific issues (hence why we have
> cpu_do_idle() to abstract that)"

Wouldn't you suffer from this here as well? Anyway, the inline assembly above 
is what is actually wfi but using CP15. I checked several proc-*.S in do_idle 
and they all have
> "mcr     p15, 0, r0, c7, c0, 4           @ Wait for interrupt"
at some point. so this inline assembly could actually be implemented on wfi() 
macro.

Best regards,
Alexander

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[PATCH v2 2/2] ARM: at91: pm: switch to the PIE infrastructure Alexandre Belloni <alexandre.belloni@free-electrons.com> - 2016-06-29 00:50 +0200
  Re: [PATCH v2 2/2] ARM: at91: pm: switch to the PIE infrastructure Alexander Stein <alexander.stein@systec-electronic.com> - 2016-06-29 08:30 +0200
    Re: [PATCH v2 2/2] ARM: at91: pm: switch to the PIE infrastructure Alexandre Belloni <alexandre.belloni@free-electrons.com> - 2016-06-29 10:00 +0200
      Re: [PATCH v2 2/2] ARM: at91: pm: switch to the PIE infrastructure Alexander Stein <alexander.stein@systec-electronic.com> - 2016-06-29 10:40 +0200

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