libata: track SLEEP state and issue SRST to wake it up

ATA devices in SLEEP mode don't respond to any commands.  SRST is
necessary to wake it up.  Till now, when a command is issued to a
device in SLEEP mode, the command times out, which makes EH reset the
device and retry the command after that, causing a long delay.

This patch makes libata track SLEEP state and issue SRST automatically
if a command is about to be issued to a device in SLEEP.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Bruce Allen <ballen@gravity.phys.uwm.edu>
Cc: Andrew Paprocki <andrew@ishiboo.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/include/linux/ata.h b/include/linux/ata.h
index 8263a7b..e21c002 100644
--- a/include/linux/ata.h
+++ b/include/linux/ata.h
@@ -180,6 +180,7 @@
 	ATA_CMD_VERIFY_EXT	= 0x42,
 	ATA_CMD_STANDBYNOW1	= 0xE0,
 	ATA_CMD_IDLEIMMEDIATE	= 0xE1,
+	ATA_CMD_SLEEP		= 0xE6,
 	ATA_CMD_INIT_DEV_PARAMS	= 0x91,
 	ATA_CMD_READ_NATIVE_MAX	= 0xF8,
 	ATA_CMD_READ_NATIVE_MAX_EXT = 0x27,