gpio / ACPI: Add support for ACPI GPIO operation regions

GPIO operation regions is a new feature introduced in ACPI 5.0
specification. This feature adds a way for platform ASL code to call back
to OS GPIO driver and toggle GPIO pins.

An example ASL code from Lenovo Miix 2 tablet with only relevant part
listed:

 Device (\_SB.GPO0)
 {
     Name (AVBL, Zero)
     Method (_REG, 2, NotSerialized)
     {
         If (LEqual (Arg0, 0x08))
         {
             // Marks the region available
             Store (Arg1, AVBL)
         }
     }

     OperationRegion (GPOP, GeneralPurposeIo, Zero, 0x0C)
     Field (GPOP, ByteAcc, NoLock, Preserve)
     {
         Connection (
             GpioIo (Exclusive, PullDefault, 0, 0, IoRestrictionOutputOnly,
                     "\\_SB.GPO0", 0x00, ResourceConsumer,,)
             {
                 0x003B
             }
         ),
         SHD3,   1,
     }
 }

 Device (SHUB)
 {
     Method (_PS0, 0, Serialized)
     {
         If (LEqual (\_SB.GPO0.AVBL, One))
         {
             Store (One, \_SB.GPO0.SHD3)
             Sleep (0x32)
         }
     }
     Method (_PS3, 0, Serialized)
     {
         If (LEqual (\_SB.GPO0.AVBL, One))
         {
             Store (Zero, \_SB.GPO0.SHD3)
         }
     }
 }

How this works is that whenever _PS0 or _PS3 method is run (typically when
SHUB device is transitioned to D0 or D3 respectively), ASL code checks if
the GPIO operation region is available (\_SB.GPO0.AVBL). If it is we go and
store either 0 or 1 to \_SB.GPO0.SHD3.

Now, when ACPICA notices ACPI GPIO operation region access (the store
above) it will call acpi_gpio_adr_space_handler() that then toggles the
GPIO accordingly using standard gpiolib interfaces.

Implement the support by registering GPIO operation region handlers for all
GPIO devices that have an ACPI handle. First time the GPIO is used by the
ASL code we make sure that the GPIO stays requested until the GPIO chip
driver itself is unloaded. If we find out that the GPIO is already
requested we just toggle it according to the value got from ASL code.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib-acpi.c

@@ -16,6 +16,7 @@
 #include <linux/export.h>
 #include <linux/acpi.h>
 #include <linux/interrupt.h>
+#include <linux/mutex.h>
 
 #include "gpiolib.h"
 
@@ -26,7 +27,20 @@ struct acpi_gpio_event {
 	unsigned int irq;
 };
 
+struct acpi_gpio_connection {
+	struct list_head node;
+	struct gpio_desc *desc;
+};
+
 struct acpi_gpio_chip {
+	/*
+	 * ACPICA requires that the first field of the context parameter
+	 * passed to acpi_install_address_space_handler() is large enough
+	 * to hold struct acpi_connection_info.
+	 */
+	struct acpi_connection_info conn_info;
+	struct list_head conns;
+	struct mutex conn_lock;
 	struct gpio_chip *chip;
 	struct list_head events;
 };
@@ -334,6 +348,153 @@ struct gpio_desc *acpi_get_gpiod_by_index(struct device *dev, int index,
 	return lookup.desc ? lookup.desc : ERR_PTR(-ENOENT);
 }
 
+static acpi_status
+acpi_gpio_adr_space_handler(u32 function, acpi_physical_address address,
+			    u32 bits, u64 *value, void *handler_context,
+			    void *region_context)
+{
+	struct acpi_gpio_chip *achip = region_context;
+	struct gpio_chip *chip = achip->chip;
+	struct acpi_resource_gpio *agpio;
+	struct acpi_resource *ares;
+	acpi_status status;
+	bool pull_up;
+	int i;
+
+	status = acpi_buffer_to_resource(achip->conn_info.connection,
+					 achip->conn_info.length, &ares);
+	if (ACPI_FAILURE(status))
+		return status;
+
+	if (WARN_ON(ares->type != ACPI_RESOURCE_TYPE_GPIO)) {
+		ACPI_FREE(ares);
+		return AE_BAD_PARAMETER;
+	}
+
+	agpio = &ares->data.gpio;
+	pull_up = agpio->pin_config == ACPI_PIN_CONFIG_PULLUP;
+
+	if (WARN_ON(agpio->io_restriction == ACPI_IO_RESTRICT_INPUT &&
+	    function == ACPI_WRITE)) {
+		ACPI_FREE(ares);
+		return AE_BAD_PARAMETER;
+	}
+
+	for (i = 0; i < agpio->pin_table_length; i++) {
+		unsigned pin = agpio->pin_table[i];
+		struct acpi_gpio_connection *conn;
+		struct gpio_desc *desc;
+		bool found;
+
+		desc = gpiochip_get_desc(chip, pin);
+		if (IS_ERR(desc)) {
+			status = AE_ERROR;
+			goto out;
+		}
+
+		mutex_lock(&achip->conn_lock);
+
+		found = false;
+		list_for_each_entry(conn, &achip->conns, node) {
+			if (conn->desc == desc) {
+				found = true;
+				break;
+			}
+		}
+		if (!found) {
+			int ret;
+
+			ret = gpiochip_request_own_desc(desc, "ACPI:OpRegion");
+			if (ret) {
+				status = AE_ERROR;
+				mutex_unlock(&achip->conn_lock);
+				goto out;
+			}
+
+			switch (agpio->io_restriction) {
+			case ACPI_IO_RESTRICT_INPUT:
+				gpiod_direction_input(desc);
+				break;
+			case ACPI_IO_RESTRICT_OUTPUT:
+				/*
+				 * ACPI GPIO resources don't contain an
+				 * initial value for the GPIO. Therefore we
+				 * deduce that value from the pull field
+				 * instead. If the pin is pulled up we
+				 * assume default to be high, otherwise
+				 * low.
+				 */
+				gpiod_direction_output(desc, pull_up);
+				break;
+			default:
+				/*
+				 * Assume that the BIOS has configured the
+				 * direction and pull accordingly.
+				 */
+				break;
+			}
+
+			conn = kzalloc(sizeof(*conn), GFP_KERNEL);
+			if (!conn) {
+				status = AE_NO_MEMORY;
+				gpiochip_free_own_desc(desc);
+				mutex_unlock(&achip->conn_lock);
+				goto out;
+			}
+
+			conn->desc = desc;
+			list_add_tail(&conn->node, &achip->conns);
+		}
+
+		mutex_unlock(&achip->conn_lock);
+
+		if (function == ACPI_WRITE)
+			gpiod_set_raw_value(desc, !!((1 << i) & *value));
+		else
+			*value |= gpiod_get_raw_value(desc) << i;
+	}
+
+out:
+	ACPI_FREE(ares);
+	return status;
+}
+
+static void acpi_gpiochip_request_regions(struct acpi_gpio_chip *achip)
+{
+	struct gpio_chip *chip = achip->chip;
+	acpi_handle handle = ACPI_HANDLE(chip->dev);
+	acpi_status status;
+
+	INIT_LIST_HEAD(&achip->conns);
+	mutex_init(&achip->conn_lock);
+	status = acpi_install_address_space_handler(handle, ACPI_ADR_SPACE_GPIO,
+						    acpi_gpio_adr_space_handler,
+						    NULL, achip);
+	if (ACPI_FAILURE(status))
+		dev_err(chip->dev, "Failed to install GPIO OpRegion handler\n");
+}
+
+static void acpi_gpiochip_free_regions(struct acpi_gpio_chip *achip)
+{
+	struct gpio_chip *chip = achip->chip;
+	acpi_handle handle = ACPI_HANDLE(chip->dev);
+	struct acpi_gpio_connection *conn, *tmp;
+	acpi_status status;
+
+	status = acpi_remove_address_space_handler(handle, ACPI_ADR_SPACE_GPIO,
+						   acpi_gpio_adr_space_handler);
+	if (ACPI_FAILURE(status)) {
+		dev_err(chip->dev, "Failed to remove GPIO OpRegion handler\n");
+		return;
+	}
+
+	list_for_each_entry_safe_reverse(conn, tmp, &achip->conns, node) {
+		gpiochip_free_own_desc(conn->desc);
+		list_del(&conn->node);
+		kfree(conn);
+	}
+}
+
 void acpi_gpiochip_add(struct gpio_chip *chip)
 {
 	struct acpi_gpio_chip *acpi_gpio;
@@ -361,6 +522,7 @@ void acpi_gpiochip_add(struct gpio_chip *chip)
 	}
 
 	acpi_gpiochip_request_interrupts(acpi_gpio);
+	acpi_gpiochip_request_regions(acpi_gpio);
 }
 
 void acpi_gpiochip_remove(struct gpio_chip *chip)
@@ -379,6 +541,7 @@ void acpi_gpiochip_remove(struct gpio_chip *chip)
 		return;
 	}
 
+	acpi_gpiochip_free_regions(acpi_gpio);
 	acpi_gpiochip_free_interrupts(acpi_gpio);
 
 	acpi_detach_data(handle, acpi_gpio_chip_dh);