linux-kernel - Re: [PATCH 2/5] Blackfin arch: SMP supporting patchset: Blackfin header files and machine common code

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Date:	Tue, 18 Nov 2008 22:56:29 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Bryan Wu <cooloney@...nel.org>
Cc:	torvalds@...ux-foundation.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org, Graf Yang <graf.yang@...log.com>
Subject: Re: [PATCH 2/5] Blackfin arch: SMP supporting patchset: Blackfin
 header files and machine common code

On Tue, 18 Nov 2008 17:05:05 +0800 Bryan Wu <cooloney@...nel.org> wrote:

> From: Graf Yang <graf.yang@...log.com>
> 
> Blackfin dual core BF561 processor can support SMP like features.
> https://docs.blackfin.uclinux.org/doku.php?id=linux-kernel:smp-like
> 
> In this patch, we provide SMP extend to Blackfin header files
> and machine common code
> 
>
> ...
>
> +#define atomic_add_unless(v, a, u)				\
> +({								\
> +	int c, old;						\
> +	c = atomic_read(v);					\
> +	while (c != (u) && (old = atomic_cmpxchg((v), c, c + (a))) != c) \
> +		c = old;					\
> +	c != (u);						\
> +})

The macro references its args multiple times and will do weird or
inefficient things when called with expressions which have
side-effects, or which do slow things.

>
> ...
>
> +#include <asm/system.h>		/* save_flags */
> +
> +static inline void set_bit(int nr, volatile unsigned long *addr)
>  {
>  	int *a = (int *)addr;
>  	int mask;
> @@ -57,21 +91,23 @@ static __inline__ void clear_bit(int nr, volatile unsigned long *addr)
>  	a += nr >> 5;
>  	mask = 1 << (nr & 0x1f);
>  	local_irq_save(flags);
> -	*a &= ~mask;
> +	*a |= mask;

I think you just broke clear_bit().  Maybe I'm misreading the diff.

>  	local_irq_restore(flags);
>  }
>
>
> ...
>
> +#define smp_mb__before_clear_bit()	barrier()
> +#define smp_mb__after_clear_bit()	barrier()
> +
> +static inline void __set_bit(int nr, volatile unsigned long *addr)
> +{
> +	int *a = (int *)addr;
> +	int mask;
> +
> +	a += nr >> 5;
> +	mask = 1 << (nr & 0x1f);
> +	*a |= mask;
> +}
> +
> +static inline void __clear_bit(int nr, volatile unsigned long *addr)
> +{
> +	int *a = (int *)addr;
> +	int mask;
> +
> +	a += nr >> 5;
> +	mask = 1 << (nr & 0x1f);
> +	*a &= ~mask;
> +}
> +
> +static inline void __change_bit(int nr, volatile unsigned long *addr)
> +{
> +	int mask;
> +	unsigned long *ADDR = (unsigned long *)addr;
> +
> +	ADDR += nr >> 5;
> +	mask = 1 << (nr & 31);
> +	*ADDR ^= mask;
> +}

I'm surprised there isn't any generic code which can be used for the above.

>
> ...
>

Gad what a lot of code.  I don't think I have time to read it all, sorry.
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