Re: [PATCH 2/2] dt-bindings: iio: adc: devicetree bindings for texas instruments ads7142 iio driver

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 1 May 2021 18:25:18 +0000
Jozsef Horvath <info@ministro.hu> wrote:

> This is a device tree schema for iio driver for
>  Texas Instruments ADS7142 dual-channel, programmable sensor monitor.
> 
> Datasheet: https://www.ti.com/lit/ds/symlink/ads7142.pdf
> 
> Signed-off-by: Jozsef Horvath <info@ministro.hu>
> ---
> ---
>  .../bindings/iio/adc/ti,ads7142.yaml          | 198 ++++++++++++++++++
>  1 file changed, 198 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/adc/ti,ads7142.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads7142.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads7142.yaml
> new file mode 100644
> index 000000000000..b4e752160156
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads7142.yaml
> @@ -0,0 +1,198 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: "http://devicetree.org/schemas/iio/adc/ti,ads7142.yaml#"
> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
> +
> +title: Texas Instruments ADS7142 adc driver device tree bindings
> +
> +maintainers:
> +  - József Horváth <info@ministro.hu>
> +
> +description: |
> +  This document is for describing the required device tree parameters
> +   for ads7142 adc driver.

Document describes hardware, not a particular driver.  So just refer
to the device here.  There may well be other drives in future using
the same binding (e.g. in an RTOS).

> +  The required parameters for proper operation are described below.
> +
> +  Datasheet: https://www.ti.com/lit/ds/symlink/ads7142.pdf
> +
> +  Operation modes supportedby the driver:
> +    When the 'ti,monitoring-mode' property is not present
> +      in the devicetree node definition, the driver initiates a single
> +      conversion in the device for each read request
> +      (/sys/bus/iio/devices/iio:deviceX/in_voltageY_raw).
> +      This is a one-shot conversion, and it is called
> +      "Manual Mode" in the datasheet.
> +
> +    When the 'ti,monitoring-mode' property is present
> +      in the devicetree node definition, the driver configures
> +      the device's digital window comparator and sets the device's
> +      data buffer operation mode to pre alert data mode.
> +      The driver reads the conversion result when the BUSY/RDY interrupt
> +      fires, and keeps the value until the next BUSY/RDY interrupt
> +      or the first read request
> +      (/sys/bus/iio/devices/iio:deviceX/in_voltageY_raw).
> +      The digital window comparator and hysteresis parameters
> +      can be controlled by:
> +        - the devicetree definition of channel node
> +        - iio sysfs interfaces
> +      This is event driven conversion, and is called
> +      "Autonomous Mode with Pre Alert Data" in the datasheet.
> +      This mode can be used to wake up the system with the ALERT pin,
> +      in case when the monitored voltage level is out of the configured range.

I talked about these in the driver review so look there for comments.
Short summary is this is something userspace should have control off (assuming irq
is wired up) not dt.

> +
> +properties:
> +  compatible:
> +    const: ti,ads7142
> +
> +  reg:
> +    maxItems: 1
> +
> +  interrupts:
> +    description: |
> +      The BUSY/PDY pin is used as interrupt line in autonomous monitoring mode.
> +    maxItems: 1
> +
> +  vref-supply:
> +    description: Regulator for the reference voltage
> +
> +  power-supply: true

These don't match the naming on the pin diagram.

> +
> +  "#address-cells":
> +    const: 1
> +
> +  "#size-cells":
> +    const: 0
> +
> +  "#io-channel-cells":
> +    const: 1
> +
> +  ti,osc-sel:
> +    description: |
> +      If present, the driver selects the high speed oscillator.
> +      See chapter 7.3.5 Oscillator and Timing Control in datasheet.
> +    type: boolean

This looks connected to the possible sampling frequencies when in various autonomous modes.
Should it be controlled by userspace?

> +
> +  ti,n-clk:
> +    description: |
> +      nCLK is number of clocks in one conversion cycle.
> +      See chapter 7.3.5 Oscillator and Timing Control in datasheet.

Sounds like a policy decision for userspace.

> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    maximum: 255
> +    minimum: 0
> +
> +  ti,monitoring-mode:
> +    description: |
> +      If present, the driver selects the autonomous monitoring mode with pre alert data.
> +      See chapter 7.4 Device Functional Modes in datasheet.

As mentioned in the driver review, this looks like something we should control from userspace
not dt to me.

> +    type: boolean
> +
> +patternProperties:
> +  "^channel@[0-1]$":
> +    $ref: "adc.yaml"
> +    type: object
> +    description: |
> +      Represents the external channels which are connected to the ADC.
> +    properties:
> +      reg:
> +        description: |
> +          The channel number.
> +        items:
> +          minimum: 0
> +          maximum: 1
> +      "ti,threshold-falling":
> +        description: The low threshold for channel

For these, we need a strong argument presented in this doc for why they are not
a question of policy (and hence why they should be in dt at all).

> +        $ref: /schemas/types.yaml#/definitions/uint32
> +        maximum: 4095
> +        minimum: 0
> +      "ti,threshold-rising":
> +        description: The high threshold for channel
> +        $ref: /schemas/types.yaml#/definitions/uint32
> +        maximum: 4095
> +        minimum: 0
> +      "ti,hysteresis":
> +        description: The hysteresis for both comparators for channel
> +        $ref: /schemas/types.yaml#/definitions/uint32
> +        maximum: 63
> +        minimum: 0
> +
> +    required:
> +      - reg
> +
> +    additionalProperties: false
> +
> +allOf:
> +  - if:
> +      required:
> +        - ti,monitoring-mode
> +    then:
> +      required:
> +        - interrupts
> +
> +required:
> +  - compatible
> +  - "#io-channel-cells"
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    i2c {
> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      adc@18 {

I would not bother having two examples.  The second one covers more things afterall
and the binding makes it clear what is required.

> +        compatible = "ti,ads7142";
> +        reg = <0x18>;
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +        #io-channel-cells = <1>;
> +
> +        vref-supply = <&vdd_3v3_reg>;
> +        power-supply = <&vdd_1v8_reg>;
> +
> +        channel@0 {
> +          reg = <0>;
> +        };
> +
> +        channel@1 {
> +          reg = <1>;
> +        };
> +      };
> +    };
> +  - |
> +    i2c {
> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      adc@1f {
> +        compatible = "ti,ads7142";
> +        reg = <0x1f>;
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        #io-channel-cells = <1>;
> +
> +        vref-supply = <&vdd_3v3_reg>;
> +        power-supply = <&vdd_1v8_reg>;
> +
> +        interrupt-parent = <&gpio>;
> +        interrupts = <7 2>;
> +
> +        ti,monitoring-mode;
> +
> +        channel@0 {
> +          reg = <0>;
> +          ti,threshold-falling = <1000>;
> +          ti,threshold-rising = <2000>;
> +          ti,hysteresis = <20>;
> +        };
> +
> +        channel@1 {
> +          reg = <1>;
> +          ti,threshold-falling = <100>;
> +          ti,threshold-rising = <2500>;
> +          ti,hysteresis = <0>;
> +        };
> +      };
> +    };
> +...
> +