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

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Date:	Wed, 19 Nov 2008 15:52:50 +0800
From:	gyang <graf.yang@...log.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Bryan Wu <cooloney@...nel.org>, torvalds@...ux-foundation.org,
	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] Blackfin arch: SMP supporting patchset: Blackfin
	header files and machine common code


在 2008-11-18二的 22:56 -0800，Andrew Morton写道：
> 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.
OK, We have corrected it on our own tree.
> 
> >  	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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