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List:       linux-kernel
Subject:    Re: [PATCH] Document Linux's memory barriers [try #4]
From:       Michael Buesch <mbuesch () freenet ! de>
Date:       2006-03-10 0:07:46
Message-ID: 200603100107.46655.mbuesch () freenet ! de
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On Friday 10 March 2006 00:56, you wrote:
> 
> On Fri, 10 Mar 2006, Michael Buesch wrote:
> > 
> > So what about:
> > 
> > #define spin_lock_mmio(lock)	spin_lock(lock)
> > #define spin_unlock_mmio(lock)	do { spin_unlock(lock); mmiowb(); } while (0)
> 
> You need to put the mmiowb() inside the spinlock.

Ok, sorry. That was a typo.
I should not do more than 3 things at the same time. :)

> Yes, that is painful. But the point being that if it's outside, then when 
> somebody else gets the lock, the previous lock-owners MMIO stores may 
> still be in flight, which is what you didn't want in the first place.
> 
> Anyway, no need to make a new name for it, since you might as well just 
> use the mmiowb() explicitly. At least until this has been shown to be a 
> really common pattern (it clearly isn't, right now ;)

Ok, so maybe it is best if every device creates its own macros
for convenience (if needed => if it is a common pattern
in the scope of the driver).

Example:
#define bcm43xx_lock(bcm, flags)	spin_lock_irqsave(&(bcm)->lock, flags)
#define bcm43xx_unlock(bcm, flags)	do { mmiowb(); \
spin_unlock_irqrestore(&(bcm)->lock, flags); } while (0)

-- 
Greetings Michael.


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