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>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 25d8d3f778a1c980f5537f64648ef69d0d3a911b..2cf8251728d23f11d479c789b5f020dc9158da4b 100644 (file)
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -1410,7 +1410,16 @@ int ata_dev_read_id(struct ata_device *dev, unsigned int *p_class,
        }
 
        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);