1 files changed, 59 insertions, 54 deletions

diff --git a/drivers/acpi/events/evmisc.c b/drivers/acpi/events/evmisc.c
index bf63edc6608..f82b81cc183 100644
--- a/drivers/acpi/events/evmisc.c
+++ b/drivers/acpi/events/evmisc.c
@@ -298,19 +298,13 @@ static void ACPI_SYSTEM_XFACE acpi_ev_global_lock_thread(void *context)
 {
 	acpi_status status;
 
-	/* Signal threads that are waiting for the lock */
+	/* Signal the thread that is waiting for the lock */
 
-	if (acpi_gbl_global_lock_thread_count) {
+	/* Send a unit to the semaphore */
 
-		/* Send sufficient units to the semaphore */
-
-		status =
-		    acpi_os_signal_semaphore(acpi_gbl_global_lock_semaphore,
-					     acpi_gbl_global_lock_thread_count);
-		if (ACPI_FAILURE(status)) {
-			ACPI_ERROR((AE_INFO,
-				    "Could not signal Global Lock semaphore"));
-		}
+	status = acpi_os_signal_semaphore(acpi_gbl_global_lock_semaphore, 1);
+	if (ACPI_FAILURE(status)) {
+		ACPI_ERROR((AE_INFO, "Could not signal Global Lock semaphore"));
 	}
 }
 
@@ -333,7 +327,8 @@ static u32 acpi_ev_global_lock_handler(void *context)
 	u8 acquired = FALSE;
 
 	/*
-	 * Attempt to get the lock
+	 * Attempt to get the lock.
+	 *
 	 * If we don't get it now, it will be marked pending and we will
 	 * take another interrupt when it becomes free.
 	 */
@@ -341,6 +336,7 @@ static u32 acpi_ev_global_lock_handler(void *context)
 	if (acquired) {
 
 		/* Got the lock, now wake all threads waiting for it */
+
 		acpi_gbl_global_lock_acquired = TRUE;
 		acpi_ev_global_lock_thread(context);
 	}
@@ -399,6 +395,16 @@ acpi_status acpi_ev_init_global_lock_handler(void)
  *
  * DESCRIPTION: Attempt to gain ownership of the Global Lock.
  *
+ * MUTEX:       Interpreter must be locked
+ *
+ * Note: The original implementation allowed multiple threads to "acquire" the
+ * Global Lock, and the OS would hold the lock until the last thread had
+ * released it. However, this could potentially starve the BIOS out of the
+ * lock, especially in the case where there is a tight handshake between the
+ * Embedded Controller driver and the BIOS. Therefore, this implementation
+ * allows only one thread to acquire the HW Global Lock at a time, and makes
+ * the global lock appear as a standard mutex on the OS side.
+ *
  *****************************************************************************/
 
 acpi_status acpi_ev_acquire_global_lock(u16 timeout)
@@ -408,27 +414,25 @@ acpi_status acpi_ev_acquire_global_lock(u16 timeout)
 
 	ACPI_FUNCTION_TRACE(ev_acquire_global_lock);
 
-#ifndef ACPI_APPLICATION
-	/* Make sure that we actually have a global lock */
-
-	if (!acpi_gbl_global_lock_present) {
-		return_ACPI_STATUS(AE_NO_GLOBAL_LOCK);
+	/*
+	 * Only one thread can acquire the GL at a time, the global_lock_mutex
+	 * enforces this. This interface releases the interpreter if we must wait.
+	 */
+	status = acpi_ex_system_wait_mutex(acpi_gbl_global_lock_mutex, timeout);
+	if (ACPI_FAILURE(status)) {
+		return_ACPI_STATUS(status);
 	}
-#endif
-
-	/* One more thread wants the global lock */
-
-	acpi_gbl_global_lock_thread_count++;
 
 	/*
-	 * If we (OS side vs. BIOS side) have the hardware lock already,
-	 * we are done
+	 * Make sure that a global lock actually exists. If not, just treat
+	 * the lock as a standard mutex.
 	 */
-	if (acpi_gbl_global_lock_acquired) {
+	if (!acpi_gbl_global_lock_present) {
+		acpi_gbl_global_lock_acquired = TRUE;
 		return_ACPI_STATUS(AE_OK);
 	}
 
-	/* We must acquire the actual hardware lock */
+	/* Attempt to acquire the actual hardware lock */
 
 	ACPI_ACQUIRE_GLOBAL_LOCK(acpi_gbl_common_fACS.global_lock, acquired);
 	if (acquired) {
@@ -436,25 +440,24 @@ acpi_status acpi_ev_acquire_global_lock(u16 timeout)
 		/* We got the lock */
 
 		ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
-				  "Acquired the HW Global Lock\n"));
+				  "Acquired hardware Global Lock\n"));
 
 		acpi_gbl_global_lock_acquired = TRUE;
 		return_ACPI_STATUS(AE_OK);
 	}
 
 	/*
-	 * Did not get the lock.  The pending bit was set above, and we must now
+	 * Did not get the lock. The pending bit was set above, and we must now
 	 * wait until we get the global lock released interrupt.
 	 */
-	ACPI_DEBUG_PRINT((ACPI_DB_EXEC, "Waiting for the HW Global Lock\n"));
+	ACPI_DEBUG_PRINT((ACPI_DB_EXEC, "Waiting for hardware Global Lock\n"));
 
 	/*
-	 * Acquire the global lock semaphore first.
-	 * Since this wait will block, we must release the interpreter
+	 * Wait for handshake with the global lock interrupt handler.
+	 * This interface releases the interpreter if we must wait.
 	 */
-	status =
-	    acpi_ex_system_wait_semaphore(acpi_gbl_global_lock_semaphore,
-					  timeout);
+	status = acpi_ex_system_wait_semaphore(acpi_gbl_global_lock_semaphore,
+					       ACPI_WAIT_FOREVER);
 	return_ACPI_STATUS(status);
 }
 
@@ -477,38 +480,40 @@ acpi_status acpi_ev_release_global_lock(void)
 
 	ACPI_FUNCTION_TRACE(ev_release_global_lock);
 
-	if (!acpi_gbl_global_lock_thread_count) {
+	/* Lock must be acquired */
+
+	if (!acpi_gbl_global_lock_acquired) {
 		ACPI_WARNING((AE_INFO,
-			      "Cannot release HW Global Lock, it has not been acquired"));
+			      "Cannot release the ACPI Global Lock, it has not been acquired"));
 		return_ACPI_STATUS(AE_NOT_ACQUIRED);
 	}
 
-	/* One fewer thread has the global lock */
+	if (acpi_gbl_global_lock_present) {
 
-	acpi_gbl_global_lock_thread_count--;
-	if (acpi_gbl_global_lock_thread_count) {
+		/* Allow any thread to release the lock */
 
-		/* There are still some threads holding the lock, cannot release */
+		ACPI_RELEASE_GLOBAL_LOCK(acpi_gbl_common_fACS.global_lock,
+					 pending);
 
-		return_ACPI_STATUS(AE_OK);
+		/*
+		 * If the pending bit was set, we must write GBL_RLS to the control
+		 * register
+		 */
+		if (pending) {
+			status =
+			    acpi_set_register(ACPI_BITREG_GLOBAL_LOCK_RELEASE,
+					      1, ACPI_MTX_LOCK);
+		}
+
+		ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
+				  "Released hardware Global Lock\n"));
 	}
 
-	/*
-	 * No more threads holding lock, we can do the actual hardware
-	 * release
-	 */
-	ACPI_RELEASE_GLOBAL_LOCK(acpi_gbl_common_fACS.global_lock, pending);
 	acpi_gbl_global_lock_acquired = FALSE;
 
-	/*
-	 * If the pending bit was set, we must write GBL_RLS to the control
-	 * register
-	 */
-	if (pending) {
-		status = acpi_set_register(ACPI_BITREG_GLOBAL_LOCK_RELEASE,
-					   1, ACPI_MTX_LOCK);
-	}
+	/* Release the local GL mutex */
 
+	acpi_os_release_mutex(acpi_gbl_global_lock_mutex);
 	return_ACPI_STATUS(status);
 }