[PATCH/RFC] libata-dev: handle ERR=1 DRQ=1

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

handle ERR=1 DRQ=1 for PIO protocol

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

Some PIO read commands might set DRQ=1 alone with ERR=1.
Under such situation, the data block should be transferred even if err=1.

This patch adds extra logic to HSM_ST_ERR to handle the required
data transfer.

BTW, also found the following work in progress:
"Disable Data Transfer after Error Detection"
http://t13.org/docs2006/dt1825Lr3-DDT_TR.pdf
If this feature is turned on, then DRQ will be guaranteed 0 when ERR=1
which would simplify the PIO error handling.

Patch against the irq-pio branch.
Need your review and advice, thanks.

Albert


--- irq-pio-printk/drivers/scsi/libata-core.c	2006-03-21 17:55:35.000000000 +0800
+++ irq-pio-err/drivers/scsi/libata-core.c	2006-03-21 19:09:38.000000000 +0800
@@ -3684,6 +3684,46 @@ fsm_start:
 			printk(KERN_ERR "ata%u: command error, drv_stat 0x%x\n",
 			       ap->id, status);
 
+		/* handle ERR=1 DRQ=1 */
+		if ((status & ATA_ERR) && (status & ATA_DRQ)) {
+			/* ERR=1 DRQ=1 is only possible for reads (READ PIO
+			 * and READ MULTI, etc). For writes, DRQ=1 doesn't
+			 * make sense since the data block has been
+			 * transferred to the device.
+			 */
+			if ((qc->tf.protocol == ATA_PROT_PIO) &&
+			    !(qc->tf.flags & ATA_TFLAG_WRITE)) {
+				/* Transfer the corrupted data */
+				ata_pio_sectors(qc);
+
+				/* FIXME: contents of taskfile registers
+				 * undefined after the data xfer.
+				 * Maybe we should call ->tf_read()
+				 * and backup the taskfile somewhere?
+				 * Otherwise ata_gen_fixed_sense() won't
+				 * get needed information.
+				 */
+
+				/* FIXME: The spec said if "correctable"
+				 * data error, subsequent blocks will
+				 * be transferred. Isn't the command
+				 * stopped if ERR is set?
+				 */
+
+				ata_altstatus(ap); /* flush */
+				status = ata_chk_status(ap);
+
+				printk(KERN_ERR "ata%u: ERR=1 DRQ=1 error"
+				       " block transferred, drv_stat 0x%x\n",
+				       ap->id, status);
+			} else
+				/* Low possibility for other protocols
+				 * being ERR=1 DRQ=1. Maybe device error?
+				 */
+				printk(KERN_ERR "ata%u: ERR=1 DRQ=1\n",
+				       ap->id);
+		}
+
 		/* make sure qc->err_mask is available to
 		 * know what's wrong and recover
 		 */