ARM (ARM926ejs): add data cache support, tested on magnesium and tx25 board

Enable "cache" command on tx25 and magnesium board and test performance.

    Test 1: Loading 127 MB of data from NAND flash into RAM:

    Instr. Cache        off     on      on
      Data Cache        off     off     on
    --------------------------------------------------
    magnesium           32,6s   22,5s   30s     = x 1,09
    tx25 (29MB only)    9,69s   5,05s   8,16s   = x 1,19

    Test 2: uncompressing a gzipped image from RAM to RAM
            (size compressed: 6.5 MiB, uncompressed: 35 MiB):

    Instr. Cache        off     on      on
      Data Cache        off     off     on
    --------------------------------------------------
    magnesium           4,25s   2,08s   1,72s   = x 2,47
    tx25                4,82s   2,04s   1,84s   = x 2,62

Portions of this work were supported by funding from
the CE Linux Forum.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Alessandro Rubini <rubini@gnudd.com>

arch/arm/lib/cache.c

@@ -31,6 +31,12 @@ void  flush_cache (unsigned long dummy1, unsigned long dummy2)
 	void arm1136_cache_flush(void);
 
 	arm1136_cache_flush();
+#endif
+#ifdef CONFIG_ARM926EJS
+	/* test and clean, page 2-23 of arm926ejs manual */
+	asm("0: mrc p15, 0, r15, c7, c10, 3\n\t" "bne 0b\n" : : : "memory");
+	/* disable write buffer as well (page 2-22) */
+	asm("mcr p15, 0, %0, c7, c10, 4" : : "r" (0));
 #endif
 	return;
 }

include/configs/imx27lite-common.h

@@ -188,6 +188,7 @@
  */
 #include <config_cmd_default.h>
 #define CONFIG_CMD_ASKENV
+#define CONFIG_CMD_CACHE
 #define CONFIG_CMD_DHCP
 #define CONFIG_CMD_DIAG
 #define CONFIG_CMD_FAT

include/configs/tx25.h

@@ -131,6 +131,7 @@
 /* U-Boot commands */
 #include <config_cmd_default.h>
 #define CONFIG_CMD_NAND
+#define CONFIG_CMD_CACHE
 
 /*
  * Ethernet