[PATCH] libata-hp-prep: implement followup softreset handling

In some cases, hardreset must be followed by SRST.

* some controllers can't classify with hardreset
* some controllers can't wait for !BSY after hardreset (LLDD should
  explicitly request followup softreset by returning -EAGAIN)
* (later) PM needs SRST w/ PMP==15 to operate after hardreset

To handle above cases, this patch implements follow-up softreset.
After a hardreset, ata_eh_reset() checks whether any of above
conditions are met and do a follow-up softreset if necessary.

Signed-off-by: Tejun Heo <htejun@gmail.com>

drivers/scsi/libata-eh.c

@@ -1318,16 +1318,28 @@ static void ata_eh_report(struct ata_port *ap)
 	}
 }
 
-static int ata_eh_reset(struct ata_port *ap,
+static int ata_eh_followup_srst_needed(int rc, int classify,
+				       const unsigned int *classes)
+{
+	if (rc == -EAGAIN)
+		return 1;
+	if (rc != 0)
+		return 0;
+	if (classify && classes[0] == ATA_DEV_UNKNOWN)
+		return 1;
+	return 0;
+}
+
+static int ata_eh_reset(struct ata_port *ap, int classify,
 			ata_prereset_fn_t prereset, ata_reset_fn_t softreset,
 			ata_reset_fn_t hardreset, ata_postreset_fn_t postreset)
 {
 	struct ata_eh_context *ehc = &ap->eh_context;
-	unsigned int classes[ATA_MAX_DEVICES];
+	unsigned int *classes = ehc->classes;
 	int tries = ATA_EH_RESET_TRIES;
 	unsigned int action;
 	ata_reset_fn_t reset;
-	int i, rc;
+	int i, did_followup_srst, rc;
 
 	/* Determine which reset to use and record in ehc->i.action.
 	 * prereset() may examine and modify it.
@@ -1381,10 +1393,44 @@ static int ata_eh_reset(struct ata_port *ap,
 
 	rc = ata_do_reset(ap, reset, classes);
 
+	did_followup_srst = 0;
+	if (reset == hardreset &&
+	    ata_eh_followup_srst_needed(rc, classify, classes)) {
+		/* okay, let's do follow-up softreset */
+		did_followup_srst = 1;
+		reset = softreset;
+
+		if (!reset) {
+			ata_port_printk(ap, KERN_ERR,
+					"follow-up softreset required "
+					"but no softreset avaliable\n");
+			return -EINVAL;
+		}
+
+		ata_eh_about_to_do(ap, ATA_EH_RESET_MASK);
+		rc = ata_do_reset(ap, reset, classes);
+
+		if (rc == 0 && classify &&
+		    classes[0] == ATA_DEV_UNKNOWN) {
+			ata_port_printk(ap, KERN_ERR,
+					"classification failed\n");
+			return -EINVAL;
+		}
+	}
+
 	if (rc && --tries) {
+		const char *type;
+
+		if (reset == softreset) {
+			if (did_followup_srst)
+				type = "follow-up soft";
+			else
+				type = "soft";
+		} else
+			type = "hard";
+
 		ata_port_printk(ap, KERN_WARNING,
-				"%sreset failed, retrying in 5 secs\n",
-				reset == softreset ? "soft" : "hard");
+				"%sreset failed, retrying in 5 secs\n", type);
 		ssleep(5);
 
 		if (reset == hardreset)
@@ -1508,7 +1554,7 @@ static int ata_eh_recover(struct ata_port *ap, ata_prereset_fn_t prereset,
 	if (ehc->i.action & ATA_EH_RESET_MASK) {
 		ata_eh_freeze_port(ap);
 
-		rc = ata_eh_reset(ap, prereset, softreset, hardreset,
+		rc = ata_eh_reset(ap, 0, prereset, softreset, hardreset,
 				  postreset);
 		if (rc) {
 			ata_port_printk(ap, KERN_ERR,