pinctrl: freescale: imx: imx7d iomuxc-lpsr devicetree bindings

Add iomuxc-lpsr devicetree bindings documentation
Provide documentation context as well an example on
pheriperals that could use pad from either iomuxc controller
supported by iMX7D SoC
Signed-off-by: Adrian Alonso <aalonso@freescale.com>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/fsl,imx7d-pinctrl.txt

 * Freescale i.MX7 Dual IOMUX Controller
 
+iMX7D supports two iomuxc controllers, fsl,imx7d-iomuxc controller is similar
+as previous iMX SoC generation and fsl,imx7d-iomuxc-lpsr which provides low
+power state retention capabilities on gpios that are part of iomuxc-lpsr
+(GPIO1_IO7..GPIO1_IO0). While iomuxc-lpsr provides its own set of registers for
+mux and pad control settings, it shares the input select register from main
+iomuxc controller for daisy chain settings, the fsl,input-sel property extends
+fsl,imx-pinctrl driver to support iomuxc-lpsr controller.
+
+iomuxc_lpsr: iomuxc-lpsr@302c0000 {
+	compatible = "fsl,imx7d-iomuxc-lpsr";
+	reg = <0x302c0000 0x10000>;
+	fsl,input-sel = <&iomuxc>;
+};
+
+iomuxc: iomuxc@30330000 {
+	compatible = "fsl,imx7d-iomuxc";
+	reg = <0x30330000 0x10000>;
+};
+
+Pheriparials using pads from iomuxc-lpsr support low state retention power
+state, under LPSR mode GPIO's state of pads are retain.
+
 Please refer to fsl,imx-pinctrl.txt in this directory for common binding part
 and usage.
 
 Required properties:
-- compatible: "fsl,imx7d-iomuxc"
+- compatible: "fsl,imx7d-iomuxc" for main IOMUXC controller, or
+  "fsl,imx7d-iomuxc-lpsr" for Low Power State Retention IOMUXC controller.
 - fsl,pins: each entry consists of 6 integers and represents the mux and config
   setting for one pin.  The first 5 integers <mux_reg conf_reg input_reg mux_val
   input_val> are specified using a PIN_FUNC_ID macro, which can be found in
   imx7d-pinfunc.h under device tree source folder.  The last integer CONFIG is
   the pad setting value like pull-up on this pin.  Please refer to i.MX7 Dual
   Reference Manual for detailed CONFIG settings.
+- fsl,input-sel: required property for iomuxc-lpsr controller, this property is
+  a phandle for main iomuxc controller which shares the input select register for
+  daisy chain settings.
 
 CONFIG bits definition:
 PAD_CTL_PUS_100K_DOWN           (0 << 5)
@@ -25,3 +51,38 @@ PAD_CTL_DSE_X1                  (0 << 0)
 PAD_CTL_DSE_X2                  (1 << 0)
 PAD_CTL_DSE_X3                  (2 << 0)
 PAD_CTL_DSE_X4                  (3 << 0)
+
+Examples:
+While iomuxc-lpsr is intended to be used by dedicated peripherals to take
+advantages of LPSR power mode, is also possible that an IP to use pads from
+any of the iomux controllers. For example the I2C1 IP can use SCL pad from
+iomuxc-lpsr controller and SDA pad from iomuxc controller as:
+
+i2c1: i2c@30a20000 {
+	pinctrl-names = "default";
+	pinctrl-0 = <&pinctrl_i2c1_1 &pinctrl_i2c1_2>;
+	status = "okay";
+};
+
+iomuxc-lpsr@302c0000 {
+	compatible = "fsl,imx7d-iomuxc-lpsr";
+	reg = <0x302c0000 0x10000>;
+	fsl,input-sel = <&iomuxc>;
+
+	pinctrl_i2c1_1: i2c1grp-1 {
+		fsl,pins = <
+			MX7D_PAD_GPIO1_IO04__I2C1_SCL 0x4000007f
+		>;
+	};
+};
+
+iomuxc@30330000 {
+	compatible = "fsl,imx7d-iomuxc";
+	reg = <0x30330000 0x10000>;
+
+	pinctrl_i2c1_2: i2c1grp-2 {
+		fsl,pins = <
+			MX7D_PAD_I2C1_SDA__I2C1_SDA 0x4000007f
+		>;
+	};
+};