drivers/mtd/redboot.c: recognise a foreign byte sex partition table

The RedBoot boot loader writes flash partition tables containing native
byte sex 32 bit values.  When booting an opposite byte sex kernel (e.g.  an
LE kernel from BE RedBoot) the current MTD driver fails to handle the
partition table and therefore is unable to generate the correct partition
map for the flash.

The patch recognises that the FIS directory (the partition table) is
byte-reversed by examining the partition table size, which is known to be
one erase block (this is an assumption made elsewhere in redboot.c).  If
the size matches the erase block after byte swapping the value then
byte-reversal is assumed, if not no further action is taken.  The patched
code is fail safe; should redboot.c be changed to support a partition table
with a modified size field the test will fail and the partition table will
be assumed to have the host byte sex.

If byte-reversal is detected the patch byte swaps the remainder of the 32
bit fields in the copy of the table; this copy is then used to set up the
MTD partition map.

Signed-off-by: John Bowler <jbowler@acm.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Modified slightly and
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

Index: drivers/mtd/redboot.c
===================================================================
RCS file: /home/cvs/mtd/drivers/mtd/redboot.c,v
retrieving revision 1.18
retrieving revision 1.19
diff -u -p -r1.18 -r1.19
--- linux-2.6.15/drivers/mtd/redboot.c	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.15/drivers/mtd/redboot.c	1970-01-01 00:00:00.000000000 +0000
@@ -89,8 +89,32 @@ static int parse_redboot_partitions(stru
 			i = numslots;
 			break;
 		}
-		if (!memcmp(buf[i].name, "FIS directory", 14))
+		if (!memcmp(buf[i].name, "FIS directory", 14)) {
+			/* This is apparently the FIS directory entry for the
+			 * FIS directory itself.  The FIS directory size is
+			 * one erase block; if the buf[i].size field is
+			 * swab32(erasesize) then we know we are looking at
+			 * a byte swapped FIS directory - swap all the entries!
+			 * (NOTE: this is 'size' not 'data_length'; size is
+			 * the full size of the entry.)
+			 */
+			if (swab32(buf[i].size) == master->erasesize) {
+				int j;
+				for (j = 0; j < numslots && buf[j].name[0] != 0xff; ++j) {
+					/* The unsigned long fields were written with the
+					 * wrong byte sex, name and pad have no byte sex.
+					 */
+					swab32s(&buf[j].flash_base);
+					swab32s(&buf[j].mem_base);
+					swab32s(&buf[j].size);
+					swab32s(&buf[j].entry_point);
+					swab32s(&buf[j].data_length);
+					swab32s(&buf[j].desc_cksum);
+					swab32s(&buf[j].file_cksum);
+				}
+			}
 			break;
+		}
 	}
 	if (i == numslots) {
 		/* Didn't find it */