libahci: fix turning on LEDs in ahci_start_port()

If EM Transmit bit is busy during init ata_msleep() is called.  It is
wrong - msleep() should be used instead of ata_msleep(), because if EM
Transmit bit is busy for one port, it will be busy for all other ports
too, so using ata_msleep() causes wasting tries for another ports.

The most common scenario looks like that now
(six ports try to transmit a LED meaasege):
- port #0 tries for the 1st time and succeeds
- ports #1-5 try for the 1st time and sleeps
- port #1 tries for the 2nd time and succeeds
- ports #2-5 try for the 2nd time and sleeps
- port #2 tries for the 3rd time and succeeds
- ports #3-5 try for the 3rd time and sleeps
- port #3 tries for the 4th time and succeeds
- ports #4-5 try for the 4th time and sleeps
- port #4 tries for the 5th time and succeeds
- port #5 tries for the 5th time and sleeps

At this moment port #5 wasted all its five tries and failed to
initialize.  Because there are only 5 (EM_MAX_RETRY) tries available
usually only five ports succeed to initialize. The sixth port and next
ones usually will fail.

If msleep() is used instead of ata_msleep() the first port succeeds to
initialize in the first try and next ones usually succeed to
initialize in the second try.

tj: updated comment

Signed-off-by: Lukasz Dorau <lukasz.dorau@intel.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

drivers/ata/libahci.c

@@ -778,8 +778,16 @@ static void ahci_start_port(struct ata_port *ap)
 				rc = ap->ops->transmit_led_message(ap,
 							       emp->led_state,
 							       4);
+				/*
+				 * If busy, give a breather but do not
+				 * release EH ownership by using msleep()
+				 * instead of ata_msleep().  EM Transmit
+				 * bit is busy for the whole host and
+				 * releasing ownership will cause other
+				 * ports to fail the same way.
+				 */
 				if (rc == -EBUSY)
-					ata_msleep(ap, 1);
+					msleep(1);
 				else
 					break;
 			}