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

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Message-Id: <1158010198.3879.52.camel@localhost.localdomain>
Date:	Tue, 12 Sep 2006 07:29:58 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jeff Garzik <jgarzik@...ox.com>,
	Paul Mackerras <paulus@...ba.org>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>,
	Segher Boessenkool <segher@...nel.crashing.org>
Subject: Re: [RFC] MMIO accessors & barriers documentation

On Mon, 2006-09-11 at 18:26 +0100, Alan Cox wrote:
> Ar Llu, 2006-09-11 am 19:59 +1000, ysgrifennodd Benjamin Herrenschmidt:
> > Ok, so we would define ordering on the first and last accesses (being
> > the first and last in ascending addresses order) and leave it free to
> > the implementation to do what it wants in between. Is that ok ?
> 
> Not sure you can go that far. I'd stick to "_fromio/_toio" transfer
> blocks of data efficiently between host and bus addresses. The
> guarantees are the same as readl/writel respectively with respect to the
> start and end of the transfer.
> 
> [How do you define start and end addresses with memcpy_fromio(foo, bar,
> 4) for example ]

Ok. So they behave like a writel or a readl globally respective to other
accesses but there is no guarantee in order or size of the individual
transfers making them up.

Ben


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