at91: Choose environment variables location within make config target

This patch adds the possiblity to choose the media where the environment will
be located. This allow to choose this fundamental configuration without editing
config files.

Documentation file added.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Stelian Pop <stelian@popies.net>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/include/configs/at91sam9261ek.h b/include/configs/at91sam9261ek.h
index bd66823..0016b4f 100644
--- a/include/configs/at91sam9261ek.h
+++ b/include/configs/at91sam9261ek.h
@@ -144,15 +144,12 @@
 #define CONFIG_SYS_MEMTEST_START		PHYS_SDRAM
 #define CONFIG_SYS_MEMTEST_END			0x23e00000
 
-#define CONFIG_SYS_USE_DATAFLASH_CS0		1
-#undef CONFIG_SYS_USE_NANDFLASH
-
 #ifdef CONFIG_SYS_USE_DATAFLASH_CS0
 
 /* bootstrap + u-boot + env + linux in dataflash on CS0 */
 #define CONFIG_ENV_IS_IN_DATAFLASH	1
 #define CONFIG_SYS_MONITOR_BASE	(CONFIG_SYS_DATAFLASH_LOGIC_ADDR_CS0 + 0x8400)
-#define CONFIG_ENV_OFFSET		0x4200
+#define CONFIG_ENV_OFFSET	0x4200
 #define CONFIG_ENV_ADDR		(CONFIG_SYS_DATAFLASH_LOGIC_ADDR_CS0 + CONFIG_ENV_OFFSET)
 #define CONFIG_ENV_SIZE		0x4200
 #define CONFIG_BOOTCOMMAND	"cp.b 0xC0042000 0x22000000 0x210000; bootm"
@@ -161,6 +158,20 @@
 				"mtdparts=at91_nand:-(root) "		\
 				"rw rootfstype=jffs2"
 
+#elif CONFIG_SYS_USE_DATAFLASH_CS3
+
+/* bootstrap + u-boot + env + linux in dataflash on CS3 */
+#define CONFIG_ENV_IS_IN_DATAFLASH	1
+#define CONFIG_SYS_MONITOR_BASE	(CONFIG_SYS_DATAFLASH_LOGIC_ADDR_CS3 + 0x8400)
+#define CONFIG_ENV_OFFSET	0x4200
+#define CONFIG_ENV_ADDR		(CONFIG_SYS_DATAFLASH_LOGIC_ADDR_CS3 + CONFIG_ENV_OFFSET)
+#define CONFIG_ENV_SIZE		0x4200
+#define CONFIG_BOOTCOMMAND	"cp.b 0xD0042000 0x22000000 0x210000; bootm"
+#define CONFIG_BOOTARGS		"console=ttyS0,115200 "			\
+				"root=/dev/mtdblock0 "			\
+				"mtdparts=at91_nand:-(root) "		\
+				"rw rootfstype=jffs2"
+
 #else /* CONFIG_SYS_USE_NANDFLASH */
 
 /* bootstrap + u-boot + env + linux in nandflash */