gpiolib-acpi: make sure we trigger edge events at least once on boot

On some systems using edge triggered ACPI Event Interrupts, the initial
state at boot is not setup by the firmware, instead relying on the edge
irq event handler running at least once to setup the initial state.

2 known examples of this are:

1) The Surface 3 has its _LID state controlled by an ACPI operation region
 triggered by a GPIO event:

 OperationRegion (GPOR, GeneralPurposeIo, Zero, One)
 Field (GPOR, ByteAcc, NoLock, Preserve)
 {
     Connection (
         GpioIo (Shared, PullNone, 0x0000, 0x0000, IoRestrictionNone,
             "\\_SB.GPO0", 0x00, ResourceConsumer, ,
             )
             {   // Pin list
                 0x004C
             }
     ),
     HELD,   1
 }

 Method (_E4C, 0, Serialized)  // _Exx: Edge-Triggered GPE
 {
     If ((HELD == One))
     {
         ^^LID.LIDB = One
     }
     Else
     {
         ^^LID.LIDB = Zero
         Notify (LID, 0x80) // Status Change
     }

     Notify (^^PCI0.SPI1.NTRG, One) // Device Check
 }

 Currently, the state of LIDB is wrong until the user actually closes or
 open the cover. We need to trigger the GPIO event once to update the
 internal ACPI state.

 Coincidentally, this also enables the Surface 2 integrated HID sensor hub
 which also requires an ACPI gpio operation region to start initialization.

2) Various Bay Trail based tablets come with an external USB mux and
 TI T1210B USB phy to enable USB gadget mode. The mux is controlled by a
 GPIO which is controlled by an edge triggered ACPI Event Interrupt which
 monitors the micro-USB ID pin.

 When the tablet is connected to a PC (or no cable is plugged in), the ID
 pin is high and the tablet should be in gadget mode. But the GPIO
 controlling the mux is initialized by the firmware so that the USB data
 lines are muxed to the host controller.

 This means that if the user wants to use gadget mode, the user needs to
 first plug in a host-cable to force the ID pin low and then unplug it
 and connect the tablet to a PC, to get the ACPI event handler to run and
 switch the mux to device mode,

This commit fixes both by running the event-handler once on boot.

Note that the running of the event-handler is done from a late_initcall,
this is done because the handler AML code may rely on OperationRegions
registered by other builtin drivers. This avoids errors like these:

[    0.133026] ACPI Error: No handler for Region [XSCG] ((____ptrval____)) [GenericSerialBus] (20180531/evregion-132)
[    0.133036] ACPI Error: Region GenericSerialBus (ID=9) has no handler (20180531/exfldio-265)
[    0.133046] ACPI Error: Method parse/execution failed \_SB.GPO2._E12, AE_NOT_EXIST (20180531/psparse-516)
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
[hdegoede: Document BYT USB mux reliance on initial trigger]
[hdegoede: Run event handler from a late_initcall, rather then immediately]
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib-acpi.c

@@ -25,6 +25,7 @@
 
 struct acpi_gpio_event {
 	struct list_head node;
+	struct list_head initial_sync_list;
 	acpi_handle handle;
 	unsigned int pin;
 	unsigned int irq;
@@ -50,6 +51,9 @@ struct acpi_gpio_chip {
 	struct list_head events;
 };
 
+static LIST_HEAD(acpi_gpio_initial_sync_list);
+static DEFINE_MUTEX(acpi_gpio_initial_sync_list_lock);
+
 static int acpi_gpiochip_find(struct gpio_chip *gc, void *data)
 {
 	if (!gc->parent)
@@ -85,6 +89,21 @@ static struct gpio_desc *acpi_get_gpiod(char *path, int pin)
 	return gpiochip_get_desc(chip, pin);
 }
 
+static void acpi_gpio_add_to_initial_sync_list(struct acpi_gpio_event *event)
+{
+	mutex_lock(&acpi_gpio_initial_sync_list_lock);
+	list_add(&event->initial_sync_list, &acpi_gpio_initial_sync_list);
+	mutex_unlock(&acpi_gpio_initial_sync_list_lock);
+}
+
+static void acpi_gpio_del_from_initial_sync_list(struct acpi_gpio_event *event)
+{
+	mutex_lock(&acpi_gpio_initial_sync_list_lock);
+	if (!list_empty(&event->initial_sync_list))
+		list_del_init(&event->initial_sync_list);
+	mutex_unlock(&acpi_gpio_initial_sync_list_lock);
+}
+
 static irqreturn_t acpi_gpio_irq_handler(int irq, void *data)
 {
 	struct acpi_gpio_event *event = data;
@@ -136,7 +155,7 @@ static acpi_status acpi_gpiochip_request_interrupt(struct acpi_resource *ares,
 	irq_handler_t handler = NULL;
 	struct gpio_desc *desc;
 	unsigned long irqflags;
-	int ret, pin, irq;
+	int ret, pin, irq, value;
 
 	if (!acpi_gpio_get_irq_resource(ares, &agpio))
 		return AE_OK;
@@ -167,6 +186,8 @@ static acpi_status acpi_gpiochip_request_interrupt(struct acpi_resource *ares,
 
 	gpiod_direction_input(desc);
 
+	value = gpiod_get_value(desc);
+
 	ret = gpiochip_lock_as_irq(chip, pin);
 	if (ret) {
 		dev_err(chip->parent, "Failed to lock GPIO as interrupt\n");
@@ -208,6 +229,7 @@ static acpi_status acpi_gpiochip_request_interrupt(struct acpi_resource *ares,
 	event->irq = irq;
 	event->pin = pin;
 	event->desc = desc;
+	INIT_LIST_HEAD(&event->initial_sync_list);
 
 	ret = request_threaded_irq(event->irq, NULL, handler, irqflags,
 				   "ACPI:Event", event);
@@ -222,6 +244,18 @@ static acpi_status acpi_gpiochip_request_interrupt(struct acpi_resource *ares,
 		enable_irq_wake(irq);
 
 	list_add_tail(&event->node, &acpi_gpio->events);
+
+	/*
+	 * Make sure we trigger the initial state of the IRQ when using RISING
+	 * or FALLING.  Note we run the handlers on late_init, the AML code
+	 * may refer to OperationRegions from other (builtin) drivers which
+	 * may be probed after us.
+	 */
+	if (handler == acpi_gpio_irq_handler &&
+	    (((irqflags & IRQF_TRIGGER_RISING) && value == 1) ||
+	     ((irqflags & IRQF_TRIGGER_FALLING) && value == 0)))
+		acpi_gpio_add_to_initial_sync_list(event);
+
 	return AE_OK;
 
 fail_free_event:
@@ -294,6 +328,8 @@ void acpi_gpiochip_free_interrupts(struct gpio_chip *chip)
 	list_for_each_entry_safe_reverse(event, ep, &acpi_gpio->events, node) {
 		struct gpio_desc *desc;
 
+		acpi_gpio_del_from_initial_sync_list(event);
+
 		if (irqd_is_wakeup_set(irq_get_irq_data(event->irq)))
 			disable_irq_wake(event->irq);
 
@@ -1158,3 +1194,21 @@ bool acpi_can_fallback_to_crs(struct acpi_device *adev, const char *con_id)
 
 	return con_id == NULL;
 }
+
+/* Sync the initial state of handlers after all builtin drivers have probed */
+static int acpi_gpio_initial_sync(void)
+{
+	struct acpi_gpio_event *event, *ep;
+
+	mutex_lock(&acpi_gpio_initial_sync_list_lock);
+	list_for_each_entry_safe(event, ep, &acpi_gpio_initial_sync_list,
+				 initial_sync_list) {
+		acpi_evaluate_object(event->handle, NULL, NULL, NULL);
+		list_del_init(&event->initial_sync_list);
+	}
+	mutex_unlock(&acpi_gpio_initial_sync_list_lock);
+
+	return 0;
+}
+/* We must use _sync so that this runs after the first deferred_probe run */
+late_initcall_sync(acpi_gpio_initial_sync);