linux-kernel - Re: [RFC] MMIO accessors & barriers documentation

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Date:	Tue, 12 Sep 2006 15:48:02 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Albert Cahalan <acahalan@...il.com>
Cc:	linux-kernel@...r.kernel.org, jbarnes@...tuousgeek.org,
	alan@...rguk.ukuu.org.uk, davem@...emloft.net, jgarzik@...ox.com,
	paulus@...ba.org, torvalds@...l.org, akpm@...l.org,
	segher@...nel.crashing.org
Subject: Re: [RFC] MMIO accessors & barriers documentation


> >  4- io_to_lock_wb() : This barrier provides ordering requirement #4
> > between an MMIO store and a subsequent spin_unlock(). It can be used in
> > conjunction with write accessors of Class 2 and 3.
> 
> These can really multiply: read or write, RAM and various types
> of IO space, etc.

No they can't. They are not dependent on the bus type but on the
processor memory model. Only 4 might have some more annoying
dependencies but in practice, it's still manageable. I think I've
defined the 4 base rules that are useful for drivers and the barriers
that provide them. Unless you can show me an example where something
else is needed.

> Let's have a generic arch-provided macro and let gcc do some work
> for us.
> 
> Example usage:
> fence(FENCE_READ_RAM|FENCE_READ_PCI_IO, FENCE_WRITE_PCI_MMIO);

  <snip>

That's terribly ugly imho.

Ben.


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