ACPICA: Events: Add parallel GPE handling support to fix potential redundant _Exx evaluations

There is a risk that a GPE method/handler may be invoked twice. Let's
consider a case, both GPE0(RAW_HANDLER) and GPE1(_Exx) is triggered.
 =======================================+=============================
 IRQ handler (top-half)                 |IRQ polling
 =======================================+=============================
 acpi_ev_detect_gpe()                   |
   LOCK()                               |
   READ (GPE0-7 enable/status registers)|
   ^^^^^^^^^^^^ROOT CAUSE^^^^^^^^^^^^^^^|
   Walk GPE0                            |
     UNLOCK()                           |LOCK()
     Invoke GPE0 RAW_HANDLER            |READ (GPE1 enable/status bit)
                                        |acpi_ev_gpe_dispatch(irq=false)
                                        |  CLEAR (GPE1 enable bit)
                                        |  CLEAR (GPE1 status bit)
     LOCK()                             |UNLOCK()
   Walk GPE1                            +=============================
     acpi_ev_gpe_dispatch(irq=true)     |IRQ polling (defer)
       CLEAR (GPE1 enable bit)          +=============================
       CLEAR (GPE1 status bit)          |acpi_ev_async_execute_gpe_method()
   Walk others                          |  Evaluate GPE1 _Exx
   fi                                   |  acpi_ev_async_enable_gpe()
   UNLOCK()                             |    LOCK()
 =======================================+    SET (GPE enable bit)
 IRQ handler (bottom-half)              |    UNLOCK()
 =======================================+
 acpi_ev_async_execute_gpe_method()     |
   Evaluate GPE1 _Exx                   |
   acpi_ev_async_enable_gpe()           |
     LOCK()                             |
     SET (GPE1 enable bit)              |
     UNLOCK()                           |
 =======================================+=============================

If acpi_ev_detect_gpe() is only invoked from the IRQ context, there won't be
more than one _Lxx/_Exx evaluations for one status bit flagging if the IRQ
handlers controlled by the underlying IRQ chip/driver (ex. APIC) are run in
serial. Note that, this is a known potential gap and we had an approach,
locking entire non-raw-handler processes in the top-half IRQ handler and
handling all raw-handlers out of the locked loop to be friendly to those
IRQ chip/driver. But the approach is too complicated while the issue is not
so real, thus ACPICA treated such issue (if any) as a parallelism/quality
issue of the underlying IRQ chip/driver to stop putting it on the radar.
Bug in link #1 is suspiciously reflecting the same cause, and if so, it can
also be fixed by this simpler approach.

But it will be no excuse an ACPICA problem now if ACPICA starts to poll
IRQs itself. In the changed scenario, _Exx will be evaluated from the task
context due to new ACPICA provided "polling after enabling GPEs" mechanism.
And the above figure uses edge-triggered GPEs demonstrating the possibility
of evaluating _Exx twice for one status bit flagging.

As a conclusion, there is now an increased chance of evaluating _Lxx/_Exx
more than once for one status bit flagging.

However this is still not a real problem if the _Lxx/_Exx checks the
underlying hardware IRQ reasoning and finally just changes the 2nd and the
follow-up evaluations into no-ops. Note that _Lxx should always be written
in this way as a level-trigger GPE could have it's status wrongly
duplicated by the underlying IRQ delivery mechanisms. But _Exx may have
very low quality BIOS by BIOS to trigger real issues. For example, trigger
duplicated button notifications.

To solve this issue, we need to stop reading a bunch of enable/status
register bits, but read only one GPE's enable/status bit. And GPE status
register's W1C nature ensures that acknowledging one GPE won't affect
another GPEs' status bits. Thus the hardware GPE architecture has already
provided us with the mechanism of implementing such parallelism.

So we can lock around one GPE handling process to achieve the parallelism:
1. If we can incorporate GPE enable bit check in detection and ensure the
   atomicity of the following process (top-half IRQ handler):
    READ (enable/status bit)
    if (enabled && raised)
      CLEAR (enable bit)
   and handle the GPE after this process, we can ensure that we will only
   invoke GPE handler once for one status bit flagging.
2. In addtion for edge-triggered GPEs, if we can ensure the atomicity of
   the following process (top-half IRQ handler):
    READ (enable/status bit)
    if (enabled && raised)
      CLEAR (enable bit)
      CLEAR (status bit)
   and handle the GPE after this process, we can ensure that we will only
   invoke GPE handler once for one status bit flagging.

By doing a cleanup in this way, we can remove duplicate GPE handling code
and ensure that all logics are collected in 1 function. And the function
will be safe for both IRQ interrupt and IRQ polling, and will be safe for
us to release and re-acquire acpi_gbl_gpe_lock at any time rather than raw
handler only during the top-half IRQ handler. Lv Zheng.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=196703 [#1]
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Erik Schmauss <erik.schmauss@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpica/acevents.h

@@ -103,6 +103,10 @@ struct acpi_gpe_event_info *acpi_ev_low_get_gpe_info(u32 gpe_number,
 
 acpi_status acpi_ev_finish_gpe(struct acpi_gpe_event_info *gpe_event_info);
 
+u32
+acpi_ev_detect_gpe(struct acpi_namespace_node *gpe_device,
+		   struct acpi_gpe_event_info *gpe_event_info, u32 gpe_number);
+
 /*
  * evgpeblk - Upper-level GPE block support
  */

drivers/acpi/acpica/evgpe.c

@@ -374,17 +374,12 @@ struct acpi_gpe_event_info *acpi_ev_get_gpe_event_info(acpi_handle gpe_device,
 
 u32 acpi_ev_gpe_detect(struct acpi_gpe_xrupt_info *gpe_xrupt_list)
 {
-	acpi_status status;
 	struct acpi_gpe_block_info *gpe_block;
 	struct acpi_namespace_node *gpe_device;
 	struct acpi_gpe_register_info *gpe_register_info;
 	struct acpi_gpe_event_info *gpe_event_info;
 	u32 gpe_number;
-	struct acpi_gpe_handler_info *gpe_handler_info;
 	u32 int_status = ACPI_INTERRUPT_NOT_HANDLED;
-	u8 enabled_status_byte;
-	u64 status_reg;
-	u64 enable_reg;
 	acpi_cpu_flags flags;
 	u32 i;
 	u32 j;
@@ -441,49 +436,11 @@ u32 acpi_ev_gpe_detect(struct acpi_gpe_xrupt_info *gpe_xrupt_list)
 				continue;
 			}
 
-			/* Read the Status Register */
-
-			status =
-			    acpi_hw_read(&status_reg,
-					 &gpe_register_info->status_address);
-			if (ACPI_FAILURE(status)) {
-				goto unlock_and_exit;
-			}
-
-			/* Read the Enable Register */
-
-			status =
-			    acpi_hw_read(&enable_reg,
-					 &gpe_register_info->enable_address);
-			if (ACPI_FAILURE(status)) {
-				goto unlock_and_exit;
-			}
-
-			ACPI_DEBUG_PRINT((ACPI_DB_INTERRUPTS,
-					  "Read registers for GPE %02X-%02X: Status=%02X, Enable=%02X, "
-					  "RunEnable=%02X, WakeEnable=%02X\n",
-					  gpe_register_info->base_gpe_number,
-					  gpe_register_info->base_gpe_number +
-					  (ACPI_GPE_REGISTER_WIDTH - 1),
-					  (u32)status_reg, (u32)enable_reg,
-					  gpe_register_info->enable_for_run,
-					  gpe_register_info->enable_for_wake));
-
-			/* Check if there is anything active at all in this register */
-
-			enabled_status_byte = (u8)(status_reg & enable_reg);
-			if (!enabled_status_byte) {
-
-				/* No active GPEs in this register, move on */
-
-				continue;
-			}
-
 			/* Now look at the individual GPEs in this byte register */
 
 			for (j = 0; j < ACPI_GPE_REGISTER_WIDTH; j++) {
 
-				/* Examine one GPE bit */
+				/* Detect and dispatch one GPE bit */
 
 				gpe_event_info =
 				    &gpe_block->
@@ -491,71 +448,18 @@ u32 acpi_ev_gpe_detect(struct acpi_gpe_xrupt_info *gpe_xrupt_list)
 						ACPI_GPE_REGISTER_WIDTH) + j];
 				gpe_number =
 				    j + gpe_register_info->base_gpe_number;
-
-				if (enabled_status_byte & (1 << j)) {
-
-					/* Invoke global event handler if present */
-
-					acpi_gpe_count++;
-					if (acpi_gbl_global_event_handler) {
-						acpi_gbl_global_event_handler
-						    (ACPI_EVENT_TYPE_GPE,
-						     gpe_device, gpe_number,
-						     acpi_gbl_global_event_handler_context);
-					}
-
-					/* Found an active GPE */
-
-					if (ACPI_GPE_DISPATCH_TYPE
-					    (gpe_event_info->flags) ==
-					    ACPI_GPE_DISPATCH_RAW_HANDLER) {
-
-						/* Dispatch the event to a raw handler */
-
-						gpe_handler_info =
-						    gpe_event_info->dispatch.
-						    handler;
-
-						/*
-						 * There is no protection around the namespace node
-						 * and the GPE handler to ensure a safe destruction
-						 * because:
-						 * 1. The namespace node is expected to always
-						 *    exist after loading a table.
-						 * 2. The GPE handler is expected to be flushed by
-						 *    acpi_os_wait_events_complete() before the
-						 *    destruction.
-						 */
-						acpi_os_release_lock
-						    (acpi_gbl_gpe_lock, flags);
-						int_status |=
-						    gpe_handler_info->
-						    address(gpe_device,
-							    gpe_number,
-							    gpe_handler_info->
-							    context);
-						flags =
-						    acpi_os_acquire_lock
-						    (acpi_gbl_gpe_lock);
-					} else {
-						/*
-						 * Dispatch the event to a standard handler or
-						 * method.
-						 */
-						int_status |=
-						    acpi_ev_gpe_dispatch
-						    (gpe_device, gpe_event_info,
-						     gpe_number);
-					}
-				}
+				acpi_os_release_lock(acpi_gbl_gpe_lock, flags);
+				int_status |=
+				    acpi_ev_detect_gpe(gpe_device,
+						       gpe_event_info,
+						       gpe_number);
+				flags = acpi_os_acquire_lock(acpi_gbl_gpe_lock);
 			}
 		}
 
 		gpe_block = gpe_block->next;
 	}
 
-unlock_and_exit:
-
 	acpi_os_release_lock(acpi_gbl_gpe_lock, flags);
 	return (int_status);
 }
@@ -726,6 +630,127 @@ acpi_status acpi_ev_finish_gpe(struct acpi_gpe_event_info *gpe_event_info)
 }
 
 
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ev_detect_gpe
+ *
+ * PARAMETERS:  gpe_device          - Device node. NULL for GPE0/GPE1
+ *              gpe_event_info      - Info for this GPE
+ *              gpe_number          - Number relative to the parent GPE block
+ *
+ * RETURN:      INTERRUPT_HANDLED or INTERRUPT_NOT_HANDLED
+ *
+ * DESCRIPTION: Detect and dispatch a General Purpose Event to either a function
+ *              (e.g. EC) or method (e.g. _Lxx/_Exx) handler.
+ * NOTE:        GPE is W1C, so it is possible to handle a single GPE from both
+ *              task and irq context in parallel as long as the process to
+ *              detect and mask the GPE is atomic.
+ *              However the atomicity of ACPI_GPE_DISPATCH_RAW_HANDLER is
+ *              dependent on the raw handler itself.
+ *
+ ******************************************************************************/
+
+u32
+acpi_ev_detect_gpe(struct acpi_namespace_node *gpe_device,
+		   struct acpi_gpe_event_info *gpe_event_info, u32 gpe_number)
+{
+	u32 int_status = ACPI_INTERRUPT_NOT_HANDLED;
+	u8 enabled_status_byte;
+	u64 status_reg;
+	u64 enable_reg;
+	u32 register_bit;
+	struct acpi_gpe_register_info *gpe_register_info;
+	struct acpi_gpe_handler_info *gpe_handler_info;
+	acpi_cpu_flags flags;
+	acpi_status status;
+
+	ACPI_FUNCTION_TRACE(ev_gpe_detect);
+
+	flags = acpi_os_acquire_lock(acpi_gbl_gpe_lock);
+
+	/* Get the info block for the entire GPE register */
+
+	gpe_register_info = gpe_event_info->register_info;
+
+	/* Get the register bitmask for this GPE */
+
+	register_bit = acpi_hw_get_gpe_register_bit(gpe_event_info);
+
+	/* GPE currently enabled (enable bit == 1)? */
+
+	status = acpi_hw_read(&enable_reg, &gpe_register_info->enable_address);
+	if (ACPI_FAILURE(status)) {
+		goto error_exit;
+	}
+
+	/* GPE currently active (status bit == 1)? */
+
+	status = acpi_hw_read(&status_reg, &gpe_register_info->status_address);
+	if (ACPI_FAILURE(status)) {
+		goto error_exit;
+	}
+
+	/* Check if there is anything active at all in this GPE */
+
+	ACPI_DEBUG_PRINT((ACPI_DB_INTERRUPTS,
+			  "Read registers for GPE %02X: Status=%02X, Enable=%02X, "
+			  "RunEnable=%02X, WakeEnable=%02X\n",
+			  gpe_number,
+			  (u32)(status_reg & register_bit),
+			  (u32)(enable_reg & register_bit),
+			  gpe_register_info->enable_for_run,
+			  gpe_register_info->enable_for_wake));
+
+	enabled_status_byte = (u8)(status_reg & enable_reg);
+	if (!(enabled_status_byte & register_bit)) {
+		goto error_exit;
+	}
+
+	/* Invoke global event handler if present */
+
+	acpi_gpe_count++;
+	if (acpi_gbl_global_event_handler) {
+		acpi_gbl_global_event_handler(ACPI_EVENT_TYPE_GPE,
+					      gpe_device, gpe_number,
+					      acpi_gbl_global_event_handler_context);
+	}
+
+	/* Found an active GPE */
+
+	if (ACPI_GPE_DISPATCH_TYPE(gpe_event_info->flags) ==
+	    ACPI_GPE_DISPATCH_RAW_HANDLER) {
+
+		/* Dispatch the event to a raw handler */
+
+		gpe_handler_info = gpe_event_info->dispatch.handler;
+
+		/*
+		 * There is no protection around the namespace node
+		 * and the GPE handler to ensure a safe destruction
+		 * because:
+		 * 1. The namespace node is expected to always
+		 *    exist after loading a table.
+		 * 2. The GPE handler is expected to be flushed by
+		 *    acpi_os_wait_events_complete() before the
+		 *    destruction.
+		 */
+		acpi_os_release_lock(acpi_gbl_gpe_lock, flags);
+		int_status |=
+		    gpe_handler_info->address(gpe_device, gpe_number,
+					      gpe_handler_info->context);
+		flags = acpi_os_acquire_lock(acpi_gbl_gpe_lock);
+	} else {
+		/* Dispatch the event to a standard handler or method. */
+
+		int_status |= acpi_ev_gpe_dispatch(gpe_device,
+						   gpe_event_info, gpe_number);
+	}
+
+error_exit:
+	acpi_os_release_lock(acpi_gbl_gpe_lock, flags);
+	return (int_status);
+}
+
 /*******************************************************************************
  *
  * FUNCTION:    acpi_ev_gpe_dispatch
@@ -739,8 +764,6 @@ acpi_status acpi_ev_finish_gpe(struct acpi_gpe_event_info *gpe_event_info)
  * DESCRIPTION: Dispatch a General Purpose Event to either a function (e.g. EC)
  *              or method (e.g. _Lxx/_Exx) handler.
  *
- *              This function executes at interrupt level.
- *
  ******************************************************************************/
 
 u32