hpilo: add locking comment

Add explanation about lock nesting and purpose of each lock in hpilo.

Signed-off-by: David Altobelli <david.altobelli@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 12 insertions, 1 deletions

diff --git a/drivers/misc/hpilo.h b/drivers/misc/hpilo.h
index 38576050776a..247eb386a973 100644
--- a/drivers/misc/hpilo.h
+++ b/drivers/misc/hpilo.h
@@ -44,9 +44,20 @@ struct ilo_hwinfo {
 
         struct pci_dev *ilo_dev;
 
+        /*
+         * open_lock      serializes ccb_cnt during open and close
+         * [ irq disabled ]
+         * -> alloc_lock  used when adding/removing/searching ccb_alloc,
+         *                which represents all ccbs open on the device
+         * --> fifo_lock  controls access to fifo queues shared with hw
+         *
+         * Locks must be taken in this order, but open_lock and alloc_lock
+         * are optional, they do not need to be held in order to take a
+         * lower level lock.
+         */
+        spinlock_t open_lock;
         spinlock_t alloc_lock;
         spinlock_t fifo_lock;
-        spinlock_t open_lock;
 
         struct cdev cdev;
 };