[PATCH 1/6] dt-bindings: ROHM BD79104 ADC

[Matti Vaittinen <mazziesaccount@gmail.com>]

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The ROHM BD79104 is a 12-bit, 8-channel ADC with two power supply pins,
connected to SPI. It's worth noting the IC requires SPI MODE 3, (CPHA =
1, CPOL = 1).

I used an evaluation board "BD79104FV-EVK-001" from ROHM. With this
board I had problems to have things working correctly with higher SPI
clock frequencies. I didn't do thorough testing for maximum frequency
though. First attempt was 40M, then 20M and finally 4M. With 20M it
seemed as if the read values were shifted by 1 bit. With 4M it worked
fine.

The component data-sheet is not exact what comes to the maximum SPI
frequency. It says SPI frequency is 20M - "unless othervice specified".
Additionally, it says that maximum sampling rate is 1Mhz, and since
reading a sample requires writing the channel (16 bits) and reading
data (16 bits) - we get some upper limit from this.

From the "frequency is 20M, unless othervice specified" I picked the
maximum frequency 20M - and did assumption that my problems with 20M
weren't related to the BD79104 - but to the evaluation board
"BD79104FV-EVK-001".

Add bindings for the ROHM BD79104 ADC.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
---
 .../bindings/iio/adc/rohm,bd79104.yaml        | 69 +++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/rohm,bd79104.yaml

diff --git a/Documentation/devicetree/bindings/iio/adc/rohm,bd79104.yaml b/Documentation/devicetree/bindings/iio/adc/rohm,bd79104.yaml
new file mode 100644
index 000000000000..2a8ad4fdfc6b
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/adc/rohm,bd79104.yaml
@@ -0,0 +1,69 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/rohm,bd79104.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ROHM Semiconductor BD79104 ADC
+
+maintainers:
+  - Matti Vaittinen <mazziesaccount@gmail.com>
+
+description: |
+  12 bit SPI ADC with 8 channels.
+
+properties:
+  compatible:
+    const: rohm,bd79104
+
+  reg:
+    maxItems: 1
+
+  vdd-supply: true
+  iovdd-supply: true
+
+# The component data-sheet says the frequency is 20M. I, however, found
+# that the ROHM evaluation board BD79104FV-EVK-001 had problems with 20M.
+# I have successfully used it with 4M. My _assumption_ is that this is not
+# the limitation of the component itself, but a limitation of the EVK.
+  spi-max-frequency:
+    maximum: 20000000
+
+  "#io-channel-cells":
+    const: 1
+
+  spi-cpha: true
+  spi-cpol: true
+
+required:
+  - compatible
+  - reg
+  - vdd-supply
+  - iovdd-supply
+  - spi-cpha
+  - spi-cpol
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@0 {
+            compatible = "rohm,bd79104";
+            reg = <0>;
+            vdd-supply = <&vdd_supply>;
+            iovdd-supply = <&iovdd_supply>;
+            spi-max-frequency = <4000000>;
+            spi-cpha;
+            spi-cpol;
+            #io-channel-cells = <1>;
+        };
+    };
+...
-- 
2.48.1


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