[ARM] 2911/1: ixp2000_reg_{read,write} accessors

Patch from Lennert Buytenhek

This patch:
- changes the ixp2000_reg_write accessor to take a 'volatile void *'
  instead of a 'volatile unsigned long *', which then allows passing in
  a u32 * as first argument without being greeted with a warning; and
- adds an ixp2000_reg_read accessor.
We can then use these accessors in ixp2000 code to access on-chip
peripherals, instead of directly dereferencing pointers.  This is for
use by the ixp2000 microengine driver which was recently announced on
netdev.  We can't use readl/writel on the ixp2000 since it is usually
run in big-endian mode, and on big-endian platforms, readl/writel
perform byteswapping.
A future patch will remove the readback from ixp2000_reg_write, since
it's not needed to prevent erratum #66, and add manual readbacks to the
places that need them (writes are not synchronous since we map in device
space using XCB=101 nowadays), such as interrupt disabling and GPIO
manipulation.  See also:
	http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2005-February/027084.html
Patch has been ACKed by Jeff Garzik.
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

include/asm-arm/arch-ixp2000/platform.h

@@ -31,20 +31,24 @@
 
 #include <asm/system.h>		/* Pickup local_irq_ functions */
 
-static inline void ixp2000_reg_write(volatile unsigned long *reg, unsigned long val)
+static inline void ixp2000_reg_write(volatile void *reg, unsigned long val)
 {
-	volatile unsigned long dummy;
+	unsigned long dummy;
 	unsigned long flags;
 
 	local_irq_save(flags);
-	*reg = val;
+	*((volatile unsigned long *)reg) = val;
 	barrier();
-	dummy = *reg;
+	dummy = *((volatile unsigned long *)reg);
 	local_irq_restore(flags);
 }
 #else
-#define	ixp2000_reg_write(reg, val) (*reg = val)
+static inline void ixp2000_reg_write(volatile void *reg, unsigned long val)
+{
+	*((volatile unsigned long *)reg) = val;
+}
 #endif	/* IXDP2400 || IXDP2401 */
+#define ixp2000_reg_read(reg)	(*((volatile unsigned long *)reg))
 
 /*
  * Boards may multiplex different devices on the 2nd channel of