libata: workaround DRQ=1 ERR=1 for ATAPI tape drives

After an error condition, some ATAPI tape drives set DRQ=1 together
with ERR=1 when asking the host to transfer the CDB of the next packet
command (i.e. request sense).  This patch, a revised version of
Alan/Mark's previous patch, adds ATA_HORKAGE_STUCK_ERR to workaround
the problem by ignoring the ERR bit and proceed sending the CDB.

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Mark Lord <liml@rtr.ca>
Signed-off-by: Tejun Heo <htejun@gmail.com>

drivers/ata/libata-core.c

@@ -5415,11 +5415,19 @@ fsm_start:
 		 * let the EH abort the command or reset the device.
 		 */
 		if (unlikely(status & (ATA_ERR | ATA_DF))) {
-			ata_port_printk(ap, KERN_WARNING, "DRQ=1 with device "
-					"error, dev_stat 0x%X\n", status);
-			qc->err_mask |= AC_ERR_HSM;
-			ap->hsm_task_state = HSM_ST_ERR;
-			goto fsm_start;
+			/* Some ATAPI tape drives forget to clear the ERR bit
+			 * when doing the next command (mostly request sense).
+			 * We ignore ERR here to workaround and proceed sending
+			 * the CDB.
+			 */
+			if (!(qc->dev->horkage & ATA_HORKAGE_STUCK_ERR)) {
+				ata_port_printk(ap, KERN_WARNING,
+						"DRQ=1 with device error, "
+						"dev_stat 0x%X\n", status);
+				qc->err_mask |= AC_ERR_HSM;
+				ap->hsm_task_state = HSM_ST_ERR;
+				goto fsm_start;
+			}
 		}
 
 		/* Send the CDB (atapi) or the first data block (ata pio out).

include/linux/libata.h

@@ -340,6 +340,7 @@ enum {
 	ATA_HORKAGE_HPA_SIZE	= (1 << 6),	/* native size off by one */
 	ATA_HORKAGE_IPM		= (1 << 7),	/* Link PM problems */
 	ATA_HORKAGE_IVB		= (1 << 8),	/* cbl det validity bit bugs */
+	ATA_HORKAGE_STUCK_ERR	= (1 << 9),	/* stuck ERR on next PACKET */
 
 	 /* DMA mask for user DMA control: User visible values; DO NOT
 	    renumber */