gpiolib-acpi: introduce acpi_get_gpio_by_index() helper

Instead of open-coding ACPI GPIO resource lookup in each driver, we provide
a helper function analogous to Device Tree version that allows drivers to
specify which GPIO resource they are interested (using an index to the GPIO
resources). The function then finds out the correct resource, translates
the ACPI GPIO number to the corresponding Linux GPIO number and returns
that.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/acpi/enumeration.txt

@@ -199,6 +199,8 @@ the device to the driver. For example:
 	{
 		Name (SBUF, ResourceTemplate()
 		{
+			...
+			// Used to power on/off the device
 			GpioIo (Exclusive, PullDefault, 0x0000, 0x0000,
 				IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0",
 				0x00, ResourceConsumer,,)
@@ -206,10 +208,20 @@ the device to the driver. For example:
 				// Pin List
 				0x0055
 			}
+
+			// Interrupt for the device
+			GpioInt (Edge, ActiveHigh, ExclusiveAndWake, PullNone,
+				 0x0000, "\\_SB.PCI0.GPI0", 0x00, ResourceConsumer,,)
+			{
+				// Pin list
+				0x0058
+			}
+
 			...
 
-			Return (SBUF)
 		}
+
+		Return (SBUF)
 	}
 
 These GPIO numbers are controller relative and path "\\_SB.PCI0.GPI0"
@@ -220,6 +232,24 @@ The driver can do this by including <linux/acpi_gpio.h> and then calling
 acpi_get_gpio(path, gpio). This will return the Linux GPIO number or
 negative errno if there was no translation found.
 
+In a simple case of just getting the Linux GPIO number from device
+resources one can use acpi_get_gpio_by_index() helper function. It takes
+pointer to the device and index of the GpioIo/GpioInt descriptor in the
+device resources list. For example:
+
+	int gpio_irq, gpio_power;
+	int ret;
+
+	gpio_irq = acpi_get_gpio_by_index(dev, 1, NULL);
+	if (gpio_irq < 0)
+		/* handle error */
+
+	gpio_power = acpi_get_gpio_by_index(dev, 0, NULL);
+	if (gpio_power < 0)
+		/* handle error */
+
+	/* Now we can use the GPIO numbers */
+
 Other GpioIo parameters must be converted first by the driver to be
 suitable to the gpiolib before passing them.