[PATCH v3 1/8] dt-bindings: ROHM BD79104 ADC

Matti Vaittinen
2025-04-07T10:45:12Z

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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>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

---
Revision history:
v1 =>
- No changes
---
.../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>;
+ };
+ };
+...