iio: adc: support GPIO-controlled Multiplexers ADC

The rockchip saradc controller is too scanty for some products that is
requires at least x10 channels ADC. Generally, we can use a CMOS analog
switch to extend a multi-channel ADC, eg.sgm3699. It's a quad,
bidirectional, single-pole/double-throw (SPDT) CMOS analog siwtch.

This patch implements a multiplexer ADC controller using a number of
gpio pins and parent ADC channel. It's compatible with most of CMOS
analog switch. And it provides a direct mode to get a raw data of each
muxadc channel.

/sys/bus/iio/devices/iio:device1/
|-- in_voltage_adc_brush_raw
|-- in_voltage_adc_mid_brush_raw
|-- in_voltage_adc_move_l_raw
|-- in_voltage_adc_move_r_raw
|-- in_voltage_qyxs_raw
|-- in_voltage_qzxs_raw
|-- in_voltage_yxs_raw
|-- in_voltage_zxs_raw

Change-Id: If71636d45543430e616299e6a6b91084f4f315e6
Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/iio/adc/gpio-muxadc.txt b/Documentation/devicetree/bindings/iio/adc/gpio-muxadc.txt
new file mode 100644
index 000000000000..f02502f8ab39
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/adc/gpio-muxadc.txt
@@ -0,0 +1,24 @@
+GPIO-controlled Multiplexers (MUX) A/D Converter bindings
+
+Required properties:
+- compatible: should be "gpio-muxadc" or others like below
+   - "sgm3699": for a quad, bidirectional, single-pole/double-throw (SPDT) CMOS analog switch.
+   - "sgm48752": for a dual, bidirectional, double-pole/double-throw (DPDT) CMOS analog switch.
+- io-channels: Channel node of the parent channel that has multiplexed input.
+- switch-gpios: Digital control pins to connect the parent adc channel(saradc) to the input adc channel(muxadc).
+- labels: The string list for each muxadc channel that should be placed in order.
+
+Example:
+        muxadc {
+                compatible = "sgm48752";
+                io-channels = <&saradc 4>, <&saradc 5>;
+                switch-gpios = <&gpio1 RK_PA0 GPIO_ACTIVE_HIGH>,
+                               <&gpio1 RK_PA1 GPIO_ACTIVE_HIGH>;
+                labels = "wheel_vpropi_r_adc", "wheel_vpropi_l_adc",
+                         "fan_opa_adc", "mid_opa_adc",
+                         "pump_opa_adc", "side_opa_adc",
+                         "dc24vdet_adc", "collision_det_adc_lidar";
+                pinctrl-names = "default";
+                pinctrl-0 = <&switch_gpios>;
+                status = "okay";
+        };