[SCSI] libata: reset once

Hotplug testing with libsas currently encounters a 55 second wait for
link recovery to give up.  In the case where the user trusts the
response time of their devices permit the recovery attempts to be
limited to one.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Acked-by: NJeff Garzik <jgarzik@redhat.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>

Documentation/kernel-parameters.txt

@@ -1350,6 +1350,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			* nohrst, nosrst, norst: suppress hard, soft
                           and both resets.
 
+			* rstonce: only attempt one reset during
+			  hot-unplug link recovery
+
 			* dump_id: dump IDENTIFY data.
 
 			If there are multiple matching configurations changing

drivers/ata/libata-core.c

@@ -6387,6 +6387,7 @@ static int __init ata_parse_force_one(char **cur,
 		{ "nohrst",	.lflags		= ATA_LFLAG_NO_HRST },
 		{ "nosrst",	.lflags		= ATA_LFLAG_NO_SRST },
 		{ "norst",	.lflags		= ATA_LFLAG_NO_HRST | ATA_LFLAG_NO_SRST },
+		{ "rstonce",	.lflags		= ATA_LFLAG_RST_ONCE },
 	};
 	char *start = *cur, *p = *cur;
 	char *id, *val, *endp;

drivers/ata/libata-eh.c

@@ -2623,6 +2623,8 @@ int ata_eh_reset(struct ata_link *link, int classify,
 	 */
 	while (ata_eh_reset_timeouts[max_tries] != ULONG_MAX)
 		max_tries++;
+	if (link->flags & ATA_LFLAG_RST_ONCE)
+		max_tries = 1;
 	if (link->flags & ATA_LFLAG_NO_HRST)
 		hardreset = NULL;
 	if (link->flags & ATA_LFLAG_NO_SRST)

include/linux/libata.h

@@ -184,6 +184,7 @@ enum {
 	ATA_LFLAG_DISABLED	= (1 << 6), /* link is disabled */
 	ATA_LFLAG_SW_ACTIVITY	= (1 << 7), /* keep activity stats */
 	ATA_LFLAG_NO_LPM	= (1 << 8), /* disable LPM on this link */
+	ATA_LFLAG_RST_ONCE	= (1 << 9), /* limit recovery to one reset */
 
 	/* struct ata_port flags */
 	ATA_FLAG_SLAVE_POSS	= (1 << 0), /* host supports slave dev */