dm: adc: add simple ADC uclass implementation

This commit adds:
- new uclass id: UCLASS_ADC
- new uclass driver: drivers/adc/adc-uclass.c

The new uclass's API allows for ADC operation on:
* single-channel with channel selection by a number
* multti-channel with channel selection by bit mask

ADC uclass's functions:
* single-channel:
  - adc_start_channel()        - start channel conversion
  - adc_channel_data()         - get conversion data
  - adc_channel_single_shot()  - start/get conversion data
* multi-channel:
  - adc_start_channels()       - start selected channels conversion
  - adc_channels_data()        - get conversion data
  - adc_channels_single_shot() - start/get conversion data for channels
                                 selected by bit mask
* general:
  - adc_stop()      - stop the conversion
  - adc_vdd_value() - positive reference Voltage value with polarity [uV]
  - adc_vss_value() - negative reference Voltage value with polarity [uV]
  - adc_data_mask() - conversion data bit mask

The device tree can provide below constraints/properties:
- vdd-polarity-negative: if true: Vdd = vdd-microvolts * (-1)
- vss-polarity-negative: if true: Vss = vss-microvolts * (-1)
- vdd-supply:            phandle to Vdd regulator's node
- vss-supply:            phandle to Vss regulator's node
And optional, checked only if the above corresponding, doesn't exist:
  - vdd-microvolts:      positive reference Voltage [uV]
  - vss-microvolts:      negative reference Voltage [uV]

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>

1 files changed, 62 insertions, 0 deletions

diff --git a/doc/device-tree-bindings/adc/adc.txt b/doc/device-tree-bindings/adc/adc.txt
new file mode 100644
index 0000000..463de3c
--- /dev/null
+++ b/doc/device-tree-bindings/adc/adc.txt
@@ -0,0 +1,62 @@
+ADC device binding
+
+There are no mandatory properties for ADC. However, if Voltage info is required,
+then there are two options:
+- use microvolts constraint or
+- use regulator phandle to enable/read supply's Voltage
+
+Properties and constraints:
+*optional and always checked, Voltage polarity info:
+- vdd-polarity-negative:  positive reference Voltage has a negative polarity
+- vss-polarity-negative:  negative reference Voltage has a negative polarity
+
+Chose one option, for each supply (Vdd/Vss):
+
+*optional and always checked, supply Voltage constants:
+- vdd-supply:            phandle to Vdd regulator's node
+- vss-supply:            phandle to Vss regulator's node
+
+*optional and checked only if the above corresponding, doesn't exist:
+- vdd-microvolts:        positive reference Voltage value [uV]
+- vss-microvolts:        negative reference Voltage value [uV]
+
+Example with constant 'Vdd' value:
+adc@1000000 {
+	compatible = "some-adc";
+	reg = <0xaabb000 0x100>;
+	status = "enabled";
+	vdd-microvolts = <1800000>;
+};
+
+Example of supply phandle usage, for the ADC's VDD/VSS references as below:
+   _______         _______
+  |Sandbox|       |Sandbox|
+  : PMIC  :       :  ADC  :
+  .       .       .       .
+  |       | (Vdd) |   AIN0|-->
+  |  BUCK2|-------|VDDref |
+  | (3.3V)|      _|VSSref |
+  |_______|     | |_______|
+               _|_
+
+For the above PMIC, the node can be defined as follows:
+sandbox_pmic {
+	compatible = "sandbox,pmic";
+	...
+	buck2: buck2 {
+		regulator-name = "SUPPLY_3.3V";
+		regulator-min-microvolt = <3300000>;
+		regulator-max-microvolt = <3300000>;
+	};
+	...
+};
+
+For the above ADC, the node can be defined as follows:
+adc@0 {
+	compatible = "sandbox,adc";
+	vdd-supply = <&buck2>;
+	vss-microvolts = <0>;
+};
+
+The ADC uclass code, will enable the supply before start of the conversion,
+but it will not configure the regulator settings.