pinctrl: mt8183: add DT binding document

The commit adds mt8183 compatible node in binding document.
Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
Signed-off-by: Erin Lo <erin.lo@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/pinctrl-mt8183.txt

+* Mediatek MT8183 Pin Controller
+
+The Mediatek's Pin controller is used to control SoC pins.
+
+Required properties:
+- compatible: value should be one of the following.
+	"mediatek,mt8183-pinctrl", compatible with mt8183 pinctrl.
+- gpio-controller : Marks the device node as a gpio controller.
+- #gpio-cells: number of cells in GPIO specifier. Since the generic GPIO
+  binding is used, the amount of cells must be specified as 2. See the below
+  mentioned gpio binding representation for description of particular cells.
+- gpio-ranges : gpio valid number range.
+- reg: physical address base for gpio base registers. There are 10 GPIO
+  physical address base in mt8183.
+
+Optional properties:
+- reg-names: gpio base register names. There are 10 gpio base register
+  names in mt8183. They are "iocfg0", "iocfg1", "iocfg2", "iocfg3", "iocfg4",
+  "iocfg5", "iocfg6", "iocfg7", "iocfg8", "eint".
+- interrupt-controller: Marks the device node as an interrupt controller
+- #interrupt-cells: Should be two.
+- interrupts : The interrupt outputs to sysirq.
+
+Please refer to pinctrl-bindings.txt in this directory for details of the
+common pinctrl bindings used by client devices.
+
+Subnode format
+A pinctrl node should contain at least one subnodes representing the
+pinctrl groups available on the machine. Each subnode will list the
+pins it needs, and how they should be configured, with regard to muxer
+configuration, pullups, drive strength, input enable/disable and input schmitt.
+
+    node {
+	pinmux = <PIN_NUMBER_PINMUX>;
+	GENERIC_PINCONFIG;
+    };
+
+Required properties:
+- pinmux: integer array, represents gpio pin number and mux setting.
+    Supported pin number and mux varies for different SoCs, and are defined
+    as macros in boot/dts/<soc>-pinfunc.h directly.
+
+Optional properties:
+- GENERIC_PINCONFIG: is the generic pinconfig options to use, bias-disable,
+    bias-pull-down, bias-pull-up, input-enable, input-disable, output-low,
+    output-high, input-schmitt-enable, input-schmitt-disable
+    and drive-strength are valid.
+
+    Some special pins have extra pull up strength, there are R0 and R1 pull-up
+    resistors available, but for user, it's only need to set R1R0 as 00, 01,
+    10 or 11. So It needs config "mediatek,pull-up-adv" or
+    "mediatek,pull-down-adv" to support arguments for those special pins.
+    Valid arguments are from 0 to 3.
+
+    mediatek,tdsel: An integer describing the steps for output level shifter
+      duty cycle when asserted (high pulse width adjustment). Valid arguments
+      are from 0 to 15.
+    mediatek,rdsel: An integer describing the steps for input level shifter
+      duty cycle when asserted (high pulse width adjustment). Valid arguments
+      are from 0 to 63.
+
+    When config drive-strength, it can support some arguments, such as
+    MTK_DRIVE_4mA, MTK_DRIVE_6mA, etc. See dt-bindings/pinctrl/mt65xx.h.
+    It can only support 2/4/6/8/10/12/14/16mA in mt8183.
+    For I2C pins, there are existing generic driving setup and the specific
+    driving setup. I2C pins can only support 2/4/6/8/10/12/14/16mA driving
+    adjustment in generic driving setup. But in specific driving setup,
+    they can support 0.125/0.25/0.5/1mA adjustment. If we enable specific
+    driving setup for I2C pins, the existing generic driving setup will be
+    disabled. For some special features, we need the I2C pins specific
+    driving setup. The specific driving setup is controlled by E1E0EN.
+    So we need add extra vendor driving preperty instead of
+    the generic driving property.
+    We can add "mediatek,drive-strength-adv = <XXX>;" to describe the specific
+    driving setup property. "XXX" means the value of E1E0EN. EN is 0 or 1.
+    It is used to enable or disable the specific driving setup.
+    E1E0 is used to describe the detail strength specification of the I2C pin.
+    When E1=0/E0=0, the strength is 0.125mA.
+    When E1=0/E0=1, the strength is 0.25mA.
+    When E1=1/E0=0, the strength is 0.5mA.
+    When E1=1/E0=1, the strength is 1mA.
+    So the valid arguments of "mediatek,drive-strength-adv" are from 0 to 7.
+
+Examples:
+
+#include "mt8183-pinfunc.h"
+
+...
+{
+	pio: pinctrl@10005000 {
+		compatible = "mediatek,mt8183-pinctrl";
+		reg = <0 0x10005000 0 0x1000>,
+		      <0 0x11f20000 0 0x1000>,
+		      <0 0x11e80000 0 0x1000>,
+		      <0 0x11e70000 0 0x1000>,
+		      <0 0x11e90000 0 0x1000>,
+		      <0 0x11d30000 0 0x1000>,
+		      <0 0x11d20000 0 0x1000>,
+		      <0 0x11c50000 0 0x1000>,
+		      <0 0x11f30000 0 0x1000>,
+		      <0 0x1000b000 0 0x1000>;
+		reg-names = "iocfg0", "iocfg1", "iocfg2",
+			    "iocfg3", "iocfg4", "iocfg5",
+			    "iocfg6", "iocfg7", "iocfg8",
+			    "eint";
+		gpio-controller;
+		#gpio-cells = <2>;
+		gpio-ranges = <&pio 0 0 192>;
+		interrupt-controller;
+		interrupts = <GIC_SPI 177 IRQ_TYPE_LEVEL_HIGH>;
+		#interrupt-cells = <2>;
+
+		i2c0_pins_a: i2c0 {
+			pins1 {
+				pinmux = <PINMUX_GPIO48__FUNC_SCL5>,
+					 <PINMUX_GPIO49__FUNC_SDA5>;
+				mediatek,pull-up-adv = <3>;
+				mediatek,drive-strength-adv = <7>;
+			};
+		};
+
+		i2c1_pins_a: i2c1 {
+			pins {
+				pinmux = <PINMUX_GPIO50__FUNC_SCL3>,
+					 <PINMUX_GPIO51__FUNC_SDA3>;
+				mediatek,pull-down-adv = <2>;
+				mediatek,drive-strength-adv = <4>;
+			};
+		};
+		...
+	};
+};