ACPI / gpio: Allow holes in list of GPIOs for a device

Make it possible to have an empty GPIOs in a GPIO list for device. For
example a SPI master may use both GPIOs and native pins as chip selects and
we need to be able to distinguish between the two.

This makes it mandatory to have exactly 3 arguments for GPIOs and then
converts gpiolib to use of __acpi_node_get_property_reference() instead. In
addition we make acpi_gpio_package_count() to handle holes as well (this
matches the DT version).

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>

1 files changed, 15 insertions, 0 deletions

diff --git a/Documentation/acpi/gpio-properties.txt b/Documentation/acpi/gpio-properties.txt
index 5aafe0b351a1..09cff657b82c 100644
--- a/Documentation/acpi/gpio-properties.txt
+++ b/Documentation/acpi/gpio-properties.txt
@@ -51,6 +51,21 @@ it to 1 marks the GPIO as active low.
 In our Bluetooth example the "reset-gpios" refers to the second GpioIo()
 resource, second pin in that resource with the GPIO number of 31.
 
+It is possible to leave holes in the array of GPIOs. This is useful in
+cases like with SPI host controllers where some chip selects may be
+implemented as GPIOs and some as native signals. For example a SPI host
+controller can have chip selects 0 and 2 implemented as GPIOs and 1 as
+native:
+
+  Package () {
+      "cs-gpios",
+      Package () {
+          ^GPIO, 19, 0, 0, // chip select 0: GPIO
+          0,               // chip select 1: native signal
+          ^GPIO, 20, 0, 0, // chip select 2: GPIO
+      }
+  }
+
 ACPI GPIO Mappings Provided by Drivers
 --------------------------------------