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Subject[RFC v5 4/4] gpio: dt-bindings: add gpio-mmio bindings
Date
From: Álvaro Fernández Rojas <noltari@gmail.com>

This patch adds the device tree bindings for the gpio-mmio.
The gpio-mmio is already part of a the GPIO generic library.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
---
.../devicetree/bindings/gpio/gpio-mmio.txt | 73 ++++++++++++++++++++++
1 file changed, 73 insertions(+)
create mode 100644 Documentation/devicetree/bindings/gpio/gpio-mmio.txt

diff --git a/Documentation/devicetree/bindings/gpio/gpio-mmio.txt b/Documentation/devicetree/bindings/gpio/gpio-mmio.txt
new file mode 100644
index 0000000..cc7f0b1
--- /dev/null
+++ b/Documentation/devicetree/bindings/gpio/gpio-mmio.txt
@@ -0,0 +1,73 @@
+Bindings for the generic driver for memory-mapped GPIO controllers.
+
+Required properties:
+ - compatible: should be "linux,gpio-mmio"
+ - reg-names: must contain
+ "dat" - data register
+ may contain
+ "set" - data set register
+ "clr" - data clear register
+ "dirout" - direction output register
+ "dirin" - direction input register
+ - reg: address + size pairs describing the GPIO register sets;
+ order must correspond with the order of entries in reg-names
+ - #gpio-cells = must be set to 2
+ - gpio-controller: Marks the device node as a gpio controller.
+
+Optional properties:
+ - ngpio: specifies the number of gpio mapped in the register.
+ - big-endian: force big endian register accesses.
+ - big-endian-byte-order: assign GPIOs in reverse order.
+ - unreadable-reg-set: data set register is not readable.
+ - read-output-reg-set: cache value set for reads.
+ - unreadable-reg-dir: dirout/dirin register is not readable.
+ - no-output: GPIOs are read-only.
+
+The GPIO generic library provides support for memory-mapped GPIO
+controllers. The configuration is detected by which resources are present.
+The simplest form of a GPIO controller that the driver support is just a
+single "dat" register, where GPIO state can be read and/or written.
+However, the driver supports far more:
+ - 8/16/32/64 bits registers. The number of GPIOs is automatically
+ determined by the width of the registers.
+ - GPIO controllers with clear/set registers.
+ - GPIO controllers with a single "dat" register.
+ - Big endian bits/GPIOs ordering.
+
+For setting GPIO's there are three configurations:
+ 1. single input/output register resource (named "dat"),
+ 2. set/clear pair (named "set" and "clr"),
+ 3. single output register resource and single input resource
+ ("set" and dat").
+
+For setting the GPIO direction, there are three configurations:
+ a. simple bidirectional GPIOs that requires no configuration.
+ b. an output direction register (named "dirout")
+ where a 1 bit indicates the GPIO is an output.
+ c. an input direction register (named "dirin")
+ where a 1 bit indicates the GPIO is an input.
+
+Examples:
+
+ /* Configuration for single input/output register
+ * for eight simple bidirectional GPIOs.
+ */
+ gpio_a_1 {
+ compatible = "linux,gpio-mmio";
+ reg = <0x18000000 0x1>;
+ reg-names = "dat";
+ #gpio-cells = <2>;
+ gpio-controller;
+ };
+
+ /* Configuration for set/clear pair registers with
+ * 32 output direction register GPIOs.
+ */
+ gpio_b_2 {
+ compatible = "linux,gpio-mmio";
+ reg = <0x18000000 0x4>, <0x18000010 0x4>,
+ <0x18000004 0x4>, <0x18000008 0x4>;
+ reg-names = "dat", "set", "clr", "dirout";
+ #gpio-cells = <2>;
+ gpio-controller;
+ };
--
2.8.1
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