linux-kernel - [PATCH 2] libahci: fix turning on LEDs in ahci_start

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Message-ID: <20131014161853.20775.1487.stgit@gklab-154-244.igk.intel.com>
Date:	Mon, 14 Oct 2013 18:18:53 +0200
From:	Lukasz Dorau <lukasz.dorau@...el.com>
To:	tj@...nel.org
Cc:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2] 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.

Signed-off-by: Lukasz Dorau <lukasz.dorau@...el.com>
---
 drivers/ata/libahci.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index acfd0f7..8fb7092 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -779,7 +779,11 @@ static void ahci_start_port(struct ata_port *ap)
 							       emp->led_state,
 							       4);
 				if (rc == -EBUSY)
-					ata_msleep(ap, 1);
+					/* Do not release ownership of @ap's EH,
+					 * because EM Transmit bit is busy for
+					 * all ports sharing the @ap->host.
+					 */
+					msleep(1);
 				else
 					break;
 			}

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