ACPI / EC: Add command flushing support.

This patch implements the EC command flushing support.

During the grace period indicated by EC_FLAGS_STARTED and EC_FLAGS_STOPPED,
all submitted EC command transactions can be completed and new submissions
are prevented before suspending so that the EC hardware can be ensured to
be in the idle state when the system is resumed.

There is a good indicator for flush support:
All acpi_ec_submit_request() is invoked after checking driver state with
acpi_ec_started() except the first one. This means all code paths can be
flushed as fast as possible by discarding the requests occurred after the
flush operation. The reference increased for such kind of code path is
wrapped by acpi_ec_submit_flushable_request().

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Tested-by: Ortwin Glück <odi@odi.ch>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/ec.c

@@ -145,6 +145,11 @@ static bool acpi_ec_started(struct acpi_ec *ec)
 	       !test_bit(EC_FLAGS_STOPPED, &ec->flags);
 }
 
+static bool acpi_ec_flushed(struct acpi_ec *ec)
+{
+	return ec->reference_count == 1;
+}
+
 /* --------------------------------------------------------------------------
  *                           EC Registers
  * -------------------------------------------------------------------------- */
@@ -266,6 +271,44 @@ static inline void acpi_ec_clear_gpe(struct acpi_ec *ec)
  *                           Transaction Management
  * -------------------------------------------------------------------------- */
 
+static void acpi_ec_submit_request(struct acpi_ec *ec)
+{
+	ec->reference_count++;
+	if (ec->reference_count == 1)
+		acpi_ec_enable_gpe(ec, true);
+}
+
+static void acpi_ec_complete_request(struct acpi_ec *ec)
+{
+	bool flushed = false;
+
+	ec->reference_count--;
+	if (ec->reference_count == 0)
+		acpi_ec_disable_gpe(ec, true);
+	flushed = acpi_ec_flushed(ec);
+	if (flushed)
+		wake_up(&ec->wait);
+}
+
+/*
+ * acpi_ec_submit_flushable_request() - Increase the reference count unless
+ *                                      the flush operation is not in
+ *                                      progress
+ * @ec: the EC device
+ *
+ * This function must be used before taking a new action that should hold
+ * the reference count.  If this function returns false, then the action
+ * must be discarded or it will prevent the flush operation from being
+ * completed.
+ */
+static bool acpi_ec_submit_flushable_request(struct acpi_ec *ec)
+{
+	if (!acpi_ec_started(ec))
+		return false;
+	acpi_ec_submit_request(ec);
+	return true;
+}
+
 static void acpi_ec_submit_query(struct acpi_ec *ec)
 {
 	if (!test_and_set_bit(EC_FLAGS_QUERY_PENDING, &ec->flags)) {
@@ -426,7 +469,8 @@ static int acpi_ec_transaction_unlocked(struct acpi_ec *ec,
 		udelay(ACPI_EC_MSI_UDELAY);
 	/* start transaction */
 	spin_lock_irqsave(&ec->lock, tmp);
-	if (!acpi_ec_started(ec)) {
+	/* Enable GPE for command processing (IBF=0/OBF=1) */
+	if (!acpi_ec_submit_flushable_request(ec)) {
 		ret = -EINVAL;
 		goto unlock;
 	}
@@ -441,6 +485,8 @@ static int acpi_ec_transaction_unlocked(struct acpi_ec *ec,
 	pr_debug("***** Command(%s) stopped *****\n",
 		 acpi_ec_cmd_string(t->command));
 	ec->curr = NULL;
+	/* Disable GPE for command processing (IBF=0/OBF=1) */
+	acpi_ec_complete_request(ec);
 unlock:
 	spin_unlock_irqrestore(&ec->lock, tmp);
 	return ret;
@@ -614,13 +660,25 @@ static void acpi_ec_start(struct acpi_ec *ec, bool resuming)
 	spin_lock_irqsave(&ec->lock, flags);
 	if (!test_and_set_bit(EC_FLAGS_STARTED, &ec->flags)) {
 		pr_debug("+++++ Starting EC +++++\n");
+		/* Enable GPE for event processing (SCI_EVT=1) */
 		if (!resuming)
-			acpi_ec_enable_gpe(ec, true);
+			acpi_ec_submit_request(ec);
 		pr_info("+++++ EC started +++++\n");
 	}
 	spin_unlock_irqrestore(&ec->lock, flags);
 }
 
+static bool acpi_ec_stopped(struct acpi_ec *ec)
+{
+	unsigned long flags;
+	bool flushed;
+
+	spin_lock_irqsave(&ec->lock, flags);
+	flushed = acpi_ec_flushed(ec);
+	spin_unlock_irqrestore(&ec->lock, flags);
+	return flushed;
+}
+
 static void acpi_ec_stop(struct acpi_ec *ec, bool suspending)
 {
 	unsigned long flags;
@@ -629,8 +687,12 @@ static void acpi_ec_stop(struct acpi_ec *ec, bool suspending)
 	if (acpi_ec_started(ec)) {
 		pr_debug("+++++ Stopping EC +++++\n");
 		set_bit(EC_FLAGS_STOPPED, &ec->flags);
+		spin_unlock_irqrestore(&ec->lock, flags);
+		wait_event(ec->wait, acpi_ec_stopped(ec));
+		spin_lock_irqsave(&ec->lock, flags);
+		/* Disable GPE for event processing (SCI_EVT=1) */
 		if (!suspending)
-			acpi_ec_disable_gpe(ec, true);
+			acpi_ec_complete_request(ec);
 		clear_bit(EC_FLAGS_STARTED, &ec->flags);
 		clear_bit(EC_FLAGS_STOPPED, &ec->flags);
 		pr_info("+++++ EC stopped +++++\n");

drivers/acpi/internal.h

@@ -122,6 +122,7 @@ struct acpi_ec {
 	unsigned long data_addr;
 	unsigned long global_lock;
 	unsigned long flags;
+	unsigned long reference_count;
 	struct mutex mutex;
 	wait_queue_head_t wait;
 	struct list_head list;