Subject: [RFC/PATCH 5/7] ARM: Move get_thread_info macro definition to <asm/assembler.h>

From: [email-masked] (Catalin Marinas)
Date: Thu, 13 Oct 2011 15:49:23 +0100

On Thu, Oct 13, 2011 at 03:34:20PM +0100, Russell King - ARM Linux wrote:
> On Wed, Oct 12, 2011 at 02:04:33AM -0400, gdavis at mvista.com wrote:
> > diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
> > index 78397d0..eaf4939 100644
> > --- a/arch/arm/include/asm/assembler.h
> > +++ b/arch/arm/include/asm/assembler.h
> > @@ -36,6 +36,20 @@
> >  	.endm
> >  #endif  /* !CONFIG_THUMB2_KERNEL */
> >  
> > +	.macro	preempt_disable, tsk, cnt
> > +	get_thread_info \tsk
> > +	ldr	\cnt, [\tsk, #TI_PREEMPT]
> > +	add	\cnt, \cnt, #1
> > +	str	\cnt, [\tsk, #TI_PREEMPT]
> > +	.endm
> > +
> > +	.macro	preempt_enable, tsk, cnt
> > +	get_thread_info \tsk
> > +	ldr	\cnt, [\tsk, #TI_PREEMPT]
> > +	sub	\cnt, \cnt, #1
> > +	str	\cnt, [\tsk, #TI_PREEMPT]
> > +	.endm
> > +
> >  /*
> >   * Endian independent macros for shifting bytes within registers.
> >   */
> > 
> > 
> > Not as efficient as it could be but I imagine the macros could
> > be written to support optional load of \tsk and/or optional \tmp
> > parameters to cover other common cases.
> 
> It's actually not that simple either: if you disable preemption, then you
> need to check for a preempt event after re-enabling preemption.

That's not easily possible in assembly as calling a function would
corrupt some registers. Is there any disadvantage with just doing the
equivalent of preempt_enable_no_resched() for a few asm cases where this
is needed?

-- 
Catalin