libata-pmp: clear hob for pmp register accesses

>> Mark Lord wrote:
>>> Tejun, I've added PMP to sata_mv, and am now trying to get it
>>> to work with a Marvell PM attached.
>>>
>>> And the behaviour I see is very bizarre.
>>>
>>> After hard+soft resets, the PM signature is found,
>>> and libata interrogates the PM registers.
>>>
>>> It successfully reads register 0, and then register 1.
>>> But all subsequent registers read out (incorrectly) as zeros.
...

This behavior has been confirmed by Marvell with a SATA analyzer.
The Marvell port-multiplier apparently likes to see clean HOB
information when accessing PMP registers.

Since sata_mv uses PIO shadow register access, this doesn't happen
automatically, as it might in a more purely FIS-based driver (eg. ahci).

One way to fix this is to flag these commands with ATA_TFLAG_LBA48,
forcing libata to write out the HOB fields with known (zero) values.

Signed-off-by: Saeed Bishara <[e-mail]>
Acked-by: Mark Lord <[e-mail]>
Signed-off-by: Jeff Garzik <[e-mail]>

drivers/ata/libata-pmp.c

···
 	ata_tf_init(pmp_dev, &tf);
 	tf.command = ATA_CMD_PMP_READ;
 	tf.protocol = ATA_PROT_NODATA;
-	tf.flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
+	tf.flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE | ATA_TFLAG_LBA48;
 	tf.feature = reg;
 	tf.device = link->pmp;
 
···
 	ata_tf_init(pmp_dev, &tf);
 	tf.command = ATA_CMD_PMP_WRITE;
 	tf.protocol = ATA_PROT_NODATA;
-	tf.flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
+	tf.flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE | ATA_TFLAG_LBA48;
 	tf.feature = reg;
 	tf.device = link->pmp;
 	tf.nsect = val & 0xff;