mcp23s08 spi gpio expander support

Basic driver for 8-bit SPI based MCP23S08 GPIO expander, without support for
IRQs or the shared chipselect mechanism.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: Eric Miao <eric.miao@marvell.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Philipp Zabel <philipp.zabel@gmail.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Ben Gardner <bgardner@wabtec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/spi/mcp23s08.h

@@ -0,0 +1,24 @@
+
+/* FIXME driver should be able to handle all four slaves that
+ * can be hooked up to each chipselect, as well as IRQs...
+ */
+
+struct mcp23s08_platform_data {
+	/* four slaves can share one SPI chipselect */
+	u8		slave;
+
+	/* number assigned to the first GPIO */
+	unsigned	base;
+
+	/* pins with pullups */
+	u8		pullups;
+
+	void		*context;	/* param to setup/teardown */
+
+	int		(*setup)(struct spi_device *spi,
+					int gpio, unsigned ngpio,
+					void *context);
+	int		(*teardown)(struct spi_device *spi,
+					int gpio, unsigned ngpio,
+					void *context);
+};