Merge remote-tracking branch 'libata/for-next'

[karo-tx-linux.git] / Documentation / devicetree / bindings / gpio / gpio.txt

diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
index 82d40e2505f641be635dd8769b0051508bcf0120..069cdf6f9dace228fe8fd97dc63c2d861273fc03 100644 (file)
--- a/Documentation/devicetree/bindings/gpio/gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio.txt
@@ -54,9 +54,13 @@ only uses one.
 
 gpio-specifier may encode: bank, pin position inside the bank,
 whether pin is open-drain and whether pin is logically inverted.
+
 Exact meaning of each specifier cell is controller specific, and must
-be documented in the device tree binding for the device. Use the macros
-defined in include/dt-bindings/gpio/gpio.h whenever possible:
+be documented in the device tree binding for the device.
+
+Most controllers are however specifying a generic flag bitfield
+in the last cell, so for these, use the macros defined in
+include/dt-bindings/gpio/gpio.h whenever possible:
 
 Example of a node using GPIOs:
 
@@ -67,6 +71,15 @@ Example of a node using GPIOs:
 GPIO_ACTIVE_HIGH is 0, so in this example gpio-specifier is "18 0" and encodes
 GPIO pin number, and GPIO flags as accepted by the "qe_pio_e" gpio-controller.
 
+Optional standard bitfield specifiers for the last cell:
+
+- Bit 0: 0 means active high, 1 means active low
+- Bit 1: 1 means single-ended wiring, see:
+           https://en.wikipedia.org/wiki/Single-ended_triode
+          When used with active-low, this means open drain/collector, see:
+           https://en.wikipedia.org/wiki/Open_collector
+          When used with active-high, this means open source/emitter
+
 1.1) GPIO specifier best practices
 ----------------------------------
 
@@ -118,6 +131,30 @@ Every GPIO controller node must contain both an empty "gpio-controller"
 property, and a #gpio-cells integer property, which indicates the number of
 cells in a gpio-specifier.
 
+Optionally, a GPIO controller may have a "ngpios" property. This property
+indicates the number of in-use slots of available slots for GPIOs. The
+typical example is something like this: the hardware register is 32 bits
+wide, but only 18 of the bits have a physical counterpart. The driver is
+generally written so that all 32 bits can be used, but the IP block is reused
+in a lot of designs, some using all 32 bits, some using 18 and some using
+12. In this case, setting "ngpios = <18>;" informs the driver that only the
+first 18 GPIOs, at local offset 0 .. 17, are in use.
+
+If these GPIOs do not happen to be the first N GPIOs at offset 0...N-1, an
+additional bitmask is needed to specify which GPIOs are actually in use,
+and which are dummies. The bindings for this case has not yet been
+specified, but should be specified if/when such hardware appears.
+
+Example:
+
+gpio-controller@00000000 {
+       compatible = "foo";
+       reg = <0x00000000 0x1000>;
+       gpio-controller;
+       #gpio-cells = <2>;
+       ngpios = <18>;
+}
+
 The GPIO chip may contain GPIO hog definitions. GPIO hogging is a mechanism
 providing automatic GPIO request and configuration as part of the
 gpio-controller's driver probe function.