From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Fri, 9 Jul 2010 13:16:29 +0100
Subject: [PATCH v2 3/3] ARM: Add barriers to the I/O accessors if
	ARM_DMA_MEM_BUFFERABLE
In-Reply-To: <1278675696.11895.37.camel@e102109-lin.cambridge.arm.com>
References: <20100709110350.11333.34303.stgit@e102109-lin.cambridge.arm.com>
	<20100709110814.11333.83771.stgit@e102109-lin.cambridge.arm.com>
	<1278675696.11895.37.camel@e102109-lin.cambridge.arm.com>
Message-ID: <20100709121629.GE22845@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, Jul 09, 2010 at 12:41:36PM +0100, Catalin Marinas wrote:
> This part requires a small change. It looks like the e1000e driver
> doesn't like the do {...} while (0) constructs in the write*() accessors
> (the E1000_WRITE_REG_ARRAY macro). Thanks to Giuseppe for finding this.

Hmm.  I think those additional parens in drivers/net/e1000e/hw.h should
be killed off instead.  They aren't serving any useful purpose.

In fact, this is potentially dangerous - it causes write[bwl]() not to
be 'void' - in that if you do use write[bwl]() in an expression that
wants its return value, write[bwl]() will generate a read.  (While you
might not use the value, you're relying on the compiler being able to
spot that you're not using the value.)

Keeping the do { } while() there prevents write[bwl]() being used as
an expression, and therefore avoids nasty surprises when the compiler
decides to read the register after writing.