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>

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index acfd0f711069e9da304c95179b14127e20ae1c9c..aaac4fb0d5645f8d52782fc55cb6f39da04830e7 100644 (file)
--- a/drivers/ata/libahci.c
+++ b/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;
                        }