linux-kernel - Re: [PATCH 1/2] WorkStruct: Add assign_bits() to give an atomic-bitops safe assignment

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Date:	Tue, 12 Dec 2006 22:54:44 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	David Howells <dhowells@...hat.com>
Cc:	torvalds@...l.org, akpm@...l.org, davem@...emloft.com,
	matthew@....cx, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/2] WorkStruct: Add assign_bits() to give an atomic-bitops safe assignment

On Tue, Dec 12, 2006 at 08:11:12PM +0000, David Howells wrote:
> diff --git a/include/asm-arm/bitops.h b/include/asm-arm/bitops.h
> index b41831b..5932134 100644
> --- a/include/asm-arm/bitops.h
> +++ b/include/asm-arm/bitops.h
> @@ -117,6 +117,32 @@ ____atomic_test_and_change_bit(unsigned 
>  	return res & mask;
>  }
>  
> +#if __LINUX_ARM_ARCH__ >= 6 && defined(CONFIG_CPU_32v6K)
> +static inline void assign_bits(unsigned long v, unsigned long *addr)
> +{
> +	unsigned long tmp;
> +
> +	__asm__ __volatile__("@ atomic_set\n"
> +"1:	ldrex	%0, [%1]\n"
> +"	strex	%0, %2, [%1]\n"
> +"	teq	%0, #0\n"
> +"	bne	1b"
> +	: "=&r" (tmp)
> +	: "r" (addr), "r" (v)
> +	: "cc");
> +}

This seems to be a very silly question (and I'm bound to be utterly
wrong as proven in my last round) but why are we implementing a new
set of atomic primitives which effectively do the same thing as our
existing set?

Why can't we just use atomic_t for this?

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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