linux-kernel - Re: [RFC][PATCH 00/29] Disintegrate and kill asm/system.h

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Date:	Wed, 7 Mar 2012 22:59:05 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	David Howells <dhowells@...hat.com>
Cc:	paul.gortmaker@...driver.com, hpa@...or.com,
	torvalds@...ux-foundation.org, sfr@...b.auug.org.au,
	mingo@...hat.com, tglx@...utronix.de, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [RFC][PATCH 00/29] Disintegrate and kill asm/system.h

On Wednesday 07 March 2012, David Howells wrote:
> Arnd Bergmann <arnd@...db.de> wrote:
> 
> > One part you were missing seems to be include/asm-generic/system.h, which is
> > used on openrisc and contains a lot of the things you move to other
> > places. It would be helpful to split that up as well.
> 
> Hmmm...  okay.  How that is used from an arch that doesn't have an
> asm/system.h?

We're migration towards using generic-y in arch/*/include/arm/Kbuild now.
When you create header files that have reasonable defaults that can be
shared across multiple architectures, I think you should do that for the
new header files as well.

> > >     (4) asm/atomic.h
> > >
> > >         Move xchg() and cmpxchg() here as they're full word atomic ops and
> > >         frequently used by atomic_xchg() and atomic_cmpxchg().
> > 
> > Well, the thing with xchg and cmpxchg is that they operate on arbirary-sized
> > integers, not atomic_t, unlike everything else in atomic.h.
> > 
> > Some architectures already have an asm/cmpxchg.h, which seems more appropriate
> > here.
> 
> So I saw.  It might be worth making an asm/xchg.h and asm/cmpxchg.h for each
> arch - or maybe just put both in asm/xchg.h or asm/cmpxchg.h.  Where do I
> include it from though?  One nice thing about sticking them in asm/atomic.h is
> that usually gets all instances, and they're frequently used from there.  How
> about I have asm/atomic.h #include asm/{,cmp}xchg.h?

Yes, that makes sense and is probably required anyway for the obvious implementation
of atomic_cmpxchg().

	Arnd
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