ipmi: Turn off all activity on an idle ipmi interface

The IPMI driver would wake up periodically looking for events and
watchdog pretimeouts.  If there is nothing waiting for these events,
it's really kind of pointless to be checking for them.  So modify the
driver so the message handler can pass down if it needs the lower layer
to be waiting for these.  Modify the system interface lower layer to
turn off all timer and thread activity if the upper layer doesn't need
anything and it is not currently handling messages.  And modify the
message handler to not restart the timer if its timer is not needed.

The timers and kthread will still be enabled if:
 - the SI interface is handling a message.
 - a user has enabled watching for events.
 - the IPMI watchdog timer is in use (since it uses pretimeouts).
 - the message handler is waiting on a remote response.
 - a user has registered to receive commands.

This mostly affects interfaces without interrupts.  Interfaces with
interrupts already don't use CPU in the system interface when the
interface is idle.
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/ipmi/ipmi_si_intf.c

@@ -257,6 +257,9 @@ struct smi_info {
 	/* Used to gracefully stop the timer without race conditions. */
 	atomic_t            stop_operation;
 
+	/* Are we waiting for the events, pretimeouts, received msgs? */
+	atomic_t            need_watch;
+
 	/*
 	 * The driver will disable interrupts when it gets into a
 	 * situation where it cannot handle messages due to lack of
@@ -862,6 +865,19 @@ static enum si_sm_result smi_event_handler(struct smi_info *smi_info,
 	return si_sm_result;
 }
 
+static void check_start_timer_thread(struct smi_info *smi_info)
+{
+	if (smi_info->si_state == SI_NORMAL && smi_info->curr_msg == NULL) {
+		smi_mod_timer(smi_info, jiffies + SI_TIMEOUT_JIFFIES);
+
+		if (smi_info->thread)
+			wake_up_process(smi_info->thread);
+
+		start_next_msg(smi_info);
+		smi_event_handler(smi_info, 0);
+	}
+}
+
 static void sender(void                *send_info,
 		   struct ipmi_smi_msg *msg,
 		   int                 priority)
@@ -915,15 +931,7 @@ static void sender(void                *send_info,
 	else
 		list_add_tail(&msg->link, &smi_info->xmit_msgs);
 
-	if (smi_info->si_state == SI_NORMAL && smi_info->curr_msg == NULL) {
-		smi_mod_timer(smi_info, jiffies + SI_TIMEOUT_JIFFIES);
-
-		if (smi_info->thread)
-			wake_up_process(smi_info->thread);
-
-		start_next_msg(smi_info);
-		smi_event_handler(smi_info, 0);
-	}
+	check_start_timer_thread(smi_info);
 	spin_unlock_irqrestore(&smi_info->si_lock, flags);
 }
 
@@ -1023,9 +1031,15 @@ static int ipmi_thread(void *data)
 			; /* do nothing */
 		else if (smi_result == SI_SM_CALL_WITH_DELAY && busy_wait)
 			schedule();
-		else if (smi_result == SI_SM_IDLE)
-			schedule_timeout_interruptible(100);
-		else
+		else if (smi_result == SI_SM_IDLE) {
+			if (atomic_read(&smi_info->need_watch)) {
+				schedule_timeout_interruptible(100);
+			} else {
+				/* Wait to be woken up when we are needed. */
+				__set_current_state(TASK_INTERRUPTIBLE);
+				schedule();
+			}
+		} else
 			schedule_timeout_interruptible(1);
 	}
 	return 0;
@@ -1061,6 +1075,17 @@ static void request_events(void *send_info)
 	atomic_set(&smi_info->req_events, 1);
 }
 
+static void set_need_watch(void *send_info, int enable)
+{
+	struct smi_info *smi_info = send_info;
+	unsigned long flags;
+
+	atomic_set(&smi_info->need_watch, enable);
+	spin_lock_irqsave(&smi_info->si_lock, flags);
+	check_start_timer_thread(smi_info);
+	spin_unlock_irqrestore(&smi_info->si_lock, flags);
+}
+
 static int initialized;
 
 static void smi_timeout(unsigned long data)
@@ -1212,6 +1237,7 @@ static struct ipmi_smi_handlers handlers = {
 	.get_smi_info		= get_smi_info,
 	.sender			= sender,
 	.request_events		= request_events,
+	.set_need_watch		= set_need_watch,
 	.set_maintenance_mode   = set_maintenance_mode,
 	.set_run_to_completion  = set_run_to_completion,
 	.poll			= poll,
@@ -3352,6 +3378,7 @@ static int try_smi_init(struct smi_info *new_smi)
 
 	new_smi->interrupt_disabled = 1;
 	atomic_set(&new_smi->stop_operation, 0);
+	atomic_set(&new_smi->need_watch, 0);
 	new_smi->intf_num = smi_num;
 	smi_num++;
 

include/linux/ipmi.h

@@ -237,7 +237,7 @@ int ipmi_set_maintenance_mode(ipmi_user_t user, int mode);
  * The first user that sets this to TRUE will receive all events that
  * have been queued while no one was waiting for events.
  */
-int ipmi_set_gets_events(ipmi_user_t user, int val);
+int ipmi_set_gets_events(ipmi_user_t user, bool val);
 
 /*
  * Called when a new SMI is registered.  This will also be called on

include/linux/ipmi_smi.h

@@ -109,6 +109,13 @@ struct ipmi_smi_handlers {
 	   events from the BMC we are attached to. */
 	void (*request_events)(void *send_info);
 
+	/* Called by the upper layer when some user requires that the
+	   interface watch for events, received messages, watchdog
+	   pretimeouts, or not.  Used by the SMI to know if it should
+	   watch for these.  This may be NULL if the SMI does not
+	   implement it. */
+	void (*set_need_watch)(void *send_info, int enable);
+
 	/* Called when the interface should go into "run to
 	   completion" mode.  If this call sets the value to true, the
 	   interface should make sure that all messages are flushed