ACPI: EC: Make the event work state machine visible

The EC driver uses a relatively simple state machine for the event
work handling, but it is not really straightforward to figure out.

The states are as follows:

"Ready": The event handling work can be submitted.

In this state, the EC_FLAGS_QUERY_PENDING flag is clear.

"In progress": The event handling work is pending or is being
processed. It cannot be submitted again.

In ths state, the EC_FLAGS_QUERY_PENDING flag is set and both the
events_to_process count is nonzero and the EC_FLAGS_QUERY_GUARDING
flag is clear.

"Complete": The event handling work has been completed, but it still
cannot be submitted again.

In ths state, the EC_FLAGS_QUERY_PENDING flag is set and the
events_to_process count is zero or the EC_FLAGS_QUERY_GUARDING
flag is set.

The state changes from "Ready" to "In progress" when new event is
detected by advance_transaction() and acpi_ec_submit_event() is
called by it.

Next, the state can change from "In progress" directly to "Ready" in
the following situations:

* ec_event_clearing is ACPI_EC_EVT_TIMING_STATUS and the state of
an ACPI_EC_COMMAND_QUERY transaction becomes ACPI_EC_COMMAND_POLL.

* ec_event_clearing is ACPI_EC_EVT_TIMING_QUERY and the state of
an ACPI_EC_COMMAND_QUERY transaction becomes
ACPI_EC_COMMAND_COMPLETE.

* ec_event_clearing is either ACPI_EC_EVT_TIMING_STATUS or
ACPI_EC_EVT_TIMING_QUERY and there are no more events to
process (ie. ec->events_to_process becomes 0).

If ec_event_clearing is ACPI_EC_EVT_TIMING_EVENT, however, the
state must change from "In progress" to "Complete" before it
can change to "Ready". The changes from "In progress" to
"Complete" in that case occur in the following situations:

* The state of an ACPI_EC_COMMAND_QUERY transaction becomes
ACPI_EC_COMMAND_COMPLETE.

* There are no more events to process (ie. ec->events_to_process
becomes 0).

Finally, the state changes from "Complete" to "Ready" when
advance_transaction() is invoked when the state is "Complete" and
the state of the current transaction is not ACPI_EC_COMMAND_POLL.

To make this state machine visible in the code, add a new
event_state field to struct acpi_ec and modify the code to use
it istead the EC_FLAGS_QUERY_PENDING and EC_FLAGS_QUERY_GUARDING
flags.

Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/ec.c

···
 
 enum {
 	EC_FLAGS_QUERY_ENABLED,		/* Query is enabled */
-	EC_FLAGS_QUERY_PENDING,		/* Query is pending */
-	EC_FLAGS_QUERY_GUARDING,	/* Guard for SCI_EVT check */
 	EC_FLAGS_EVENT_HANDLER_INSTALLED,	/* Event handler installed */
 	EC_FLAGS_EC_HANDLER_INSTALLED,	/* OpReg handler installed */
 	EC_FLAGS_QUERY_METHODS_INSTALLED, /* _Qxx handlers installed */
···
 	if (!acpi_ec_event_enabled(ec))
 		return false;
 
-	if (!test_and_set_bit(EC_FLAGS_QUERY_PENDING, &ec->flags)) {
+	if (ec->event_state == EC_EVENT_READY) {
 		ec_dbg_evt("Command(%s) submitted/blocked",
 			   acpi_ec_cmd_string(ACPI_EC_COMMAND_QUERY));
+
+		ec->event_state = EC_EVENT_IN_PROGRESS;
 		/*
 		 * If events_to_process is greqter than 0 at this point, the
 		 * while () loop in acpi_ec_event_handler() is still running
···
 	return true;
 }
 
+static void acpi_ec_complete_event(struct acpi_ec *ec)
+{
+	if (ec->event_state == EC_EVENT_IN_PROGRESS)
+		ec->event_state = EC_EVENT_COMPLETE;
+}
+
 static void acpi_ec_close_event(struct acpi_ec *ec)
 {
-	if (test_and_clear_bit(EC_FLAGS_QUERY_PENDING, &ec->flags))
+	if (ec->event_state != EC_EVENT_READY)
 		ec_dbg_evt("Command(%s) unblocked",
 			   acpi_ec_cmd_string(ACPI_EC_COMMAND_QUERY));
+
+	ec->event_state = EC_EVENT_READY;
 	acpi_ec_unmask_events(ec);
 }
 
···
 
 static bool acpi_ec_guard_event(struct acpi_ec *ec)
 {
-	bool guarded = true;
 	unsigned long flags;
+	bool guarded;
 
 	spin_lock_irqsave(&ec->lock, flags);
 	/*
···
 	 * evaluating _Qxx, so we need to re-check SCI_EVT after waiting an
 	 * acceptable period.
 	 *
-	 * The guarding period begins when EC_FLAGS_QUERY_PENDING is
-	 * flagged, which means SCI_EVT check has just been performed.
-	 * But if the current transaction is ACPI_EC_COMMAND_QUERY, the
-	 * guarding should have already been performed (via
-	 * EC_FLAGS_QUERY_GUARDING) and should not be applied so that the
-	 * ACPI_EC_COMMAND_QUERY transaction can be transitioned into
-	 * ACPI_EC_COMMAND_POLL state immediately.
+	 * The guarding period is applicable if the event state is not
+	 * EC_EVENT_READY, but otherwise if the current transaction is of the
+	 * ACPI_EC_COMMAND_QUERY type, the guarding should have elapsed already
+	 * and it should not be applied to let the transaction transition into
+	 * the ACPI_EC_COMMAND_POLL state immediately.
 	 */
-	if (ec_event_clearing == ACPI_EC_EVT_TIMING_STATUS ||
-	    ec_event_clearing == ACPI_EC_EVT_TIMING_QUERY ||
-	    !test_bit(EC_FLAGS_QUERY_PENDING, &ec->flags) ||
-	    (ec->curr && ec->curr->command == ACPI_EC_COMMAND_QUERY))
-		guarded = false;
+	guarded = ec_event_clearing == ACPI_EC_EVT_TIMING_EVENT &&
+		ec->event_state != EC_EVENT_READY &&
+		(!ec->curr || ec->curr->command != ACPI_EC_COMMAND_QUERY);
 	spin_unlock_irqrestore(&ec->lock, flags);
 	return guarded;
 }
···
 static inline void ec_transaction_transition(struct acpi_ec *ec, unsigned long flag)
 {
 	ec->curr->flags |= flag;
-	if (ec->curr->command == ACPI_EC_COMMAND_QUERY) {
-		if (ec_event_clearing == ACPI_EC_EVT_TIMING_STATUS &&
-		    flag == ACPI_EC_COMMAND_POLL)
+
+	if (ec->curr->command != ACPI_EC_COMMAND_QUERY)
+		return;
+
+	switch (ec_event_clearing) {
+	case ACPI_EC_EVT_TIMING_STATUS:
+		if (flag == ACPI_EC_COMMAND_POLL)
 			acpi_ec_close_event(ec);
-		if (ec_event_clearing == ACPI_EC_EVT_TIMING_QUERY &&
-		    flag == ACPI_EC_COMMAND_COMPLETE)
+
+		return;
+
+	case ACPI_EC_EVT_TIMING_QUERY:
+		if (flag == ACPI_EC_COMMAND_COMPLETE)
 			acpi_ec_close_event(ec);
-		if (ec_event_clearing == ACPI_EC_EVT_TIMING_EVENT &&
-		    flag == ACPI_EC_COMMAND_COMPLETE)
-			set_bit(EC_FLAGS_QUERY_GUARDING, &ec->flags);
+
+		return;
+
+	case ACPI_EC_EVT_TIMING_EVENT:
+		if (flag == ACPI_EC_COMMAND_COMPLETE)
+			acpi_ec_complete_event(ec);
 	}
 }
 
···
 	 */
 	if (!t || !(t->flags & ACPI_EC_COMMAND_POLL)) {
 		if (ec_event_clearing == ACPI_EC_EVT_TIMING_EVENT &&
-		    (!ec->events_to_process ||
-		     test_bit(EC_FLAGS_QUERY_GUARDING, &ec->flags))) {
-			clear_bit(EC_FLAGS_QUERY_GUARDING, &ec->flags);
+		    ec->event_state == EC_EVENT_COMPLETE)
 			acpi_ec_close_event(ec);
-		}
+
 		if (!t)
 			goto out;
 	}
···
 	 * event handling work again regardless of whether or not the query
 	 * queued up above is processed successfully.
 	 */
-	if (ec_event_clearing == ACPI_EC_EVT_TIMING_STATUS ||
-	    ec_event_clearing == ACPI_EC_EVT_TIMING_QUERY)
+	if (ec_event_clearing == ACPI_EC_EVT_TIMING_EVENT)
+		acpi_ec_complete_event(ec);
+	else
 		acpi_ec_close_event(ec);
 
 	spin_unlock_irq(&ec->lock);

drivers/acpi/internal.h

···
 /* --------------------------------------------------------------------------
                                   Embedded Controller
    -------------------------------------------------------------------------- */
+
+enum acpi_ec_event_state {
+	EC_EVENT_READY = 0,	/* Event work can be submitted */
+	EC_EVENT_IN_PROGRESS,	/* Event work is pending or being processed */
+	EC_EVENT_COMPLETE,	/* Event work processing has completed */
+};
+
 struct acpi_ec {
 	acpi_handle handle;
 	int gpe;
···
 	spinlock_t lock;
 	struct work_struct work;
 	unsigned long timestamp;
+	enum acpi_ec_event_state event_state;
 	unsigned int events_to_process;
 	unsigned int events_in_progress;
 	unsigned int queries_in_progress;