Subject: [PATCH] arm: Replace CONFIG_HAS_TLS_REG with HWCAP_TLS and check for it on V6

From: [email-masked] (Tony Lindgren)
Date: Fri, 19 Mar 2010 08:58:05 -0700

* Russell King - ARM Linux <[email-masked]> [100319 01:49]:
> On Thu, Mar 18, 2010 at 06:35:21PM -0700, Tony Lindgren wrote:
> > -#if defined(CONFIG_HAS_TLS_REG)
> > -	mcr	p15, 0, r3, c13, c0, 3		@ set TLS register
> > -#elif !defined(CONFIG_TLS_REG_EMUL)
> > -	mov	r4, #0xffff0fff
> > -	str	r3, [r4, #-15]			@ TLS val at 0xffff0ff0
> > +#if !defined(CONFIG_TLS_REG_EMUL)
> > +	ldr	r4, =elf_hwcap
> > +	ldr	r4, [r4, #0]
> > +	tst	r4, #HWCAP_TLS			@ hardware with TLS?
> 
> This is really really inefficient.  Both the second ldr and tst will stall
> the pipeline because they need to wait for the result of the precending
> ldr.  Can we do better by re-ordering some instructions?

Or set ifdef CONFIG_CPU_V6 and test for the cp15 id register every time..
 
> Also, the ifndef seems incorrect - if we have TLS_REG_EMUL we seem to omit
> all this code.

Is the current ifdef elif wrong? The current code does not seem to
do anything if TLS_REG_EMUL is set and HAS_TLS_REG is not set.
HAS_TLS_REG depends !TLS_REG_EMUL.

Regards,

Tony