[PATCH] ARM: locks: remove opencoded #16 for ticket shift

[Dave Martin]

On Mon, Jul 15, 2013 at 02:27:59PM +0100, Will Deacon wrote:
> The ticket width of our spinlocks is defined by TICKET_SHIFT, so remove
> the opencoded #16 from the trylock implementation.
> 
> Signed-off-by: Will Deacon <will.deacon at arm.com>
> ---
>  arch/arm/include/asm/spinlock.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h
> index f8b8965..fa3ccce 100644
> --- a/arch/arm/include/asm/spinlock.h
> +++ b/arch/arm/include/asm/spinlock.h
> @@ -104,11 +104,11 @@ static inline int arch_spin_trylock(arch_spinlock_t *lock)
>  		__asm__ __volatile__(
>  		"	ldrex	%0, [%3]\n"
>  		"	mov	%2, #0\n"
> -		"	subs	%1, %0, %0, ror #16\n"
> -		"	addeq	%0, %0, %4\n"
> +		"	subs	%1, %0, %0, ror %4\n"
> +		"	addeq	%0, %0, %5\n"

%5!  Argh.

>  		"	strexeq	%2, %0, [%3]"
>  		: "=&r" (slock), "=&r" (contended), "=r" (res)
> -		: "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
> +		: "r" (&lock->slock), "I" (TICKET_SHIFT), "I" (1 << TICKET_SHIFT)

I guess that should work.

Strictly speaking, "M" is the right constraint to use for explicit shift
counts, though it won't make much difference in practice.

(Unless it ICEs the compiler for you ... seems to work on the 4.6.3
GCC I have here.)

Cheers
---Dave

>  		: "cc");
>  	} while (res);
>  
> -- 
> 1.8.2.2
> 
> 
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