1 files changed, 59 insertions, 54 deletions

diff --git a/drivers/acpi/events/evmisc.c b/drivers/acpi/events/evmisc.c
index bf63edc6608d..f82b81cc1838 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);
 }