[patch 33/37] libata: clear TF before IDENTIFYing

[Greg KH <gregkh@suse.de>]

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-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Tejun Heo <htejun@gmail.com>

libata: clear TF before IDENTIFYing

Some devices chock if Feature is not clear when IDENTIFY is issued.
Set ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE for IDENTIFY such that whole
TF is cleared when reading ID data.

Kudos to Art Haas for testing various futile patches over several
months and Mark Lord for pointing out the fix.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Art Haas <ahaas@airmail.net>
Cc: Mark Lord <mlord@pobox.com>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 drivers/ata/libata-core.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -1478,7 +1478,16 @@ int ata_dev_read_id(struct ata_device *d
 	}
 
 	tf.protocol = ATA_PROT_PIO;
-	tf.flags |= ATA_TFLAG_POLLING; /* for polling presence detection */
+
+	/* Some devices choke if TF registers contain garbage.  Make
+	 * sure those are properly initialized.
+	 */
+	tf.flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
+
+	/* Device presence detection is unreliable on some
+	 * controllers.  Always poll IDENTIFY if available.
+	 */
+	tf.flags |= ATA_TFLAG_POLLING;
 
 	err_mask = ata_exec_internal(dev, &tf, NULL, DMA_FROM_DEVICE,
 				     id, sizeof(id[0]) * ATA_ID_WORDS);

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