[PATCH 2/4] libata: Clear tf before doing request sense

[Albert Lee <albertcc@tw.ibm.com>]

patch 2/4:
  Clear tf before doing request sense.

This fixes the AOpen 56X/AKH timeout problem.
(http://bugzilla.kernel.org/show_bug.cgi?id=8244)

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
---

Patch against libata-dev tree, for your review, thanks.

diff -Nrup 01_hsm_st/drivers/ata/libata-eh.c 02_aopen_rs/drivers/ata/libata-eh.c
--- 01_hsm_st/drivers/ata/libata-eh.c	2007-03-23 16:56:13.000000000 +0800
+++ 02_aopen_rs/drivers/ata/libata-eh.c	2007-03-31 01:11:01.000000000 +0800
@@ -991,18 +991,19 @@ static unsigned int atapi_eh_request_sen
 
 	DPRINTK("ATAPI request sense\n");
 
-	ata_tf_init(dev, &tf);
-
 	/* FIXME: is this needed? */
 	memset(sense_buf, 0, SCSI_SENSE_BUFFERSIZE);
 
-	/* XXX: why tf_read here? */
+	/* read error register to initialize sense_buf */
 	ap->ops->tf_read(ap, &tf);
 
 	/* fill these in, for the case where they are -not- overwritten */
 	sense_buf[0] = 0x70;
 	sense_buf[2] = tf.feature >> 4;
 
+	/* some devices time out if garbage left in tf */ 
+	ata_tf_init(dev, &tf);
+
 	memset(cdb, 0, ATAPI_CDB_LEN);
 	cdb[0] = REQUEST_SENSE;
 	cdb[4] = SCSI_SENSE_BUFFERSIZE;