nios2: add gpio support

This patch adds driver for a trivial gpio core, which is described
in http://nioswiki.com/GPIO

. It is used for gpio led and nand flash
interface in u-boot.

When CONFIG_SYS_GPIO_BASE is not defined, board may provide
its own driver.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Tested-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Scott McNutt <smcnutt@psyent.com>

arch/nios2/include/asm/gpio.h

+/*
+ * nios2 gpio driver
+ *
+ * This gpio core is described in http://nioswiki.com/GPIO
+ * bit[0] data
+ * bit[1] output enable
+ *
+ * when CONFIG_SYS_GPIO_BASE is not defined, board may provide
+ * its own driver.
+ *
+ * Copyright (C) 2010 Thomas Chou <thomas@wytron.com.tw>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef _ASM_NIOS2_GPIO_H_
+#define _ASM_NIOS2_GPIO_H_
+
+#ifdef CONFIG_SYS_GPIO_BASE
+#include <asm/io.h>
+
+static inline int gpio_direction_input(unsigned gpio)
+{
+	writel(1, CONFIG_SYS_GPIO_BASE + (gpio << 2));
+	return 0;
+}
+
+static inline int gpio_direction_output(unsigned gpio, int value)
+{
+	writel(value ? 3 : 2, CONFIG_SYS_GPIO_BASE + (gpio << 2));
+	return 0;
+}
+
+static inline int gpio_get_value(unsigned gpio)
+{
+	return readl(CONFIG_SYS_GPIO_BASE + (gpio << 2));
+}
+
+static inline void gpio_set_value(unsigned gpio, int value)
+{
+	writel(value ? 3 : 2, CONFIG_SYS_GPIO_BASE + (gpio << 2));
+}
+#else
+extern int gpio_direction_input(unsigned gpio);
+extern int gpio_direction_output(unsigned gpio, int value);
+extern int gpio_get_value(unsigned gpio);
+extern void gpio_set_value(unsigned gpio, int value);
+#endif /* CONFIG_SYS_GPIO_BASE */
+
+#endif /* _ASM_NIOS2_GPIO_H_ */