pata_it821x: resume from hibernation fails with RAID volume

Hibernation didn't work for me since I started to use IT8212 controller.
I did some debugging (booting with no_console_suspend init=/bin/sh).

Found that resume fails (2.6.28) with "serial number mismatch 'some
garbage' != 'some other garbage'" and "revalidation failed" messages.
That's because the controller firmware fills different serial number in
the IDENTIFY every boot.

The patch below fixes the resume simply clearing the serial number.  The
proper fix would be probably to fill in the serial number of the RAID
volume instead.  I assume that there must be something like that stored on
the drives but I don't know where.

Fix resume on pata_it821x RAID volume by clearing the serial number in
IDENTIFY data, which is otherwise different on each boot.
Signed-off-by: NOndrej Zary <linux@rainbow-software.org>
Acked-by: NAlan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>

drivers/ata/pata_it821x.c

@@ -557,6 +557,9 @@ static unsigned int it821x_read_id(struct ata_device *adev,
 		id[83] |= 0x4400;	/* Word 83 is valid and LBA48 */
 		id[86] |= 0x0400;	/* LBA48 on */
 		id[ATA_ID_MAJOR_VER] |= 0x1F;
+		/* Clear the serial number because it's different each boot
+		   which breaks validation on resume */
+		memset(&id[ATA_ID_SERNO], 0x20, ATA_ID_SERNO_LEN);
 	}
 	return err_mask;
 }