[libata] Issue SRST to Sil3726 PMP

Reenable sending SRST to devices connected behind a Sil3726 PMP.
This allow staggered spinups and handles drives that spins up slowly.

While the drives spin up, the PMP will not accept SRST.
Most controller reissues the reset until the drive is ready, while
some [Sil3124] returns an error.
In ata_eh_error, wait 10s before reset the ATA port and try again.
Signed-off-by: Gwendal Grignou <gwendal@google.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-eh.c

@@ -2883,7 +2883,7 @@ int ata_eh_reset(struct ata_link *link, int classify,
 	    sata_scr_read(link, SCR_STATUS, &sstatus))
 		rc = -ERESTART;
 
-	if (rc == -ERESTART || try >= max_tries) {
+	if (try >= max_tries) {
 		/*
 		 * Thaw host port even if reset failed, so that the port
 		 * can be retried on the next phy event.  This risks
@@ -2909,6 +2909,16 @@ int ata_eh_reset(struct ata_link *link, int classify,
 		ata_eh_acquire(ap);
 	}
 
+	/*
+	 * While disks spinup behind PMP, some controllers fail sending SRST.
+	 * They need to be reset - as well as the PMP - before retrying.
+	 */
+	if (rc == -ERESTART) {
+		if (ata_is_host_link(link))
+			ata_eh_thaw_port(ap);
+		goto out;
+	}
+
 	if (try == max_tries - 1) {
 		sata_down_spd_limit(link, 0);
 		if (slave)

drivers/ata/libata-pmp.c

@@ -389,12 +389,9 @@ static void sata_pmp_quirks(struct ata_port *ap)
 			/* link reports offline after LPM */
 			link->flags |= ATA_LFLAG_NO_LPM;
 
-			/* Class code report is unreliable and SRST
-			 * times out under certain configurations.
-			 */
+			/* Class code report is unreliable. */
 			if (link->pmp < 5)
-				link->flags |= ATA_LFLAG_NO_SRST |
-					       ATA_LFLAG_ASSUME_ATA;
+				link->flags |= ATA_LFLAG_ASSUME_ATA;
 
 			/* port 5 is for SEMB device and it doesn't like SRST */
 			if (link->pmp == 5)