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Message-ID: <0b3979d6-895f-4c8a-8251-d3c793385bf4@roeck-us.net>
Date: Tue, 3 Feb 2026 11:15:44 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: victor.duicu@...rochip.com
Cc: robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
corbet@....net, marius.cristea@...rochip.com,
linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
devicetree@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 1/2] dt-bindings: hwmon: add support for MCP998X
On Tue, Jan 27, 2026 at 05:18:21PM +0200, victor.duicu@...rochip.com wrote:
> From: Victor Duicu <victor.duicu@...rochip.com>
>
> This is the devicetree schema for Microchip MCP998X/33 and
> MCP998XD/33D Multichannel Automotive Temperature Monitor Family.
>
> Acked-by: Conor Dooley <conor.dooley@...rochip.com>
> Signed-off-by: Victor Duicu <victor.duicu@...rochip.com>
Some AI generated feedback inline, generated using Gemini 3 and Chris Mason's
prompts as base. I don't know much if anything about devicetree properties,
but it does seem to me that the AI has a point.
> ---
> .../bindings/hwmon/microchip,mcp9982.yaml | 205 ++++++++++++++++++
> MAINTAINERS | 6 +
> 2 files changed, 211 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/hwmon/microchip,mcp9982.yaml
>
> diff --git a/Documentation/devicetree/bindings/hwmon/microchip,mcp9982.yaml b/Documentation/devicetree/bindings/hwmon/microchip,mcp9982.yaml
> new file mode 100644
> index 000000000000..05ea3c6a5618
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/hwmon/microchip,mcp9982.yaml
> @@ -0,0 +1,205 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/hwmon/microchip,mcp9982.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Microchip MCP998X/33 and MCP998XD/33D Temperature Monitor
> +
> +maintainers:
> + - Victor Duicu <victor.duicu@...rochip.com>
> +
> +description: |
> + The MCP998X/33 and MCP998XD/33D family is a high-accuracy 2-wire
> + multichannel automotive temperature monitor.
> + The datasheet can be found here:
> + https://ww1.microchip.com/downloads/aemDocuments/documents/MSLD/ProductDocuments/DataSheets/MCP998X-Family-Data-Sheet-DS20006827.pdf
> +
> +properties:
> + compatible:
> + enum:
> + - microchip,mcp9933
> + - microchip,mcp9933d
> + - microchip,mcp9982
> + - microchip,mcp9982d
> + - microchip,mcp9983
> + - microchip,mcp9983d
> + - microchip,mcp9984
> + - microchip,mcp9984d
> + - microchip,mcp9985
> + - microchip,mcp9985d
> +
> + reg:
> + maxItems: 1
> +
> + interrupts:
> + items:
> + - description: Signal coming from ALERT/THERM pin.
> + - description: Signal coming from THERM/ADDR pin.
> + - description: Signal coming from SYS_SHDN pin.
> +
> + interrupt-names:
> + items:
> + - const: alert-therm
> + - const: therm-addr
> + - const: sys-shutdown
The top-level definition of interrupt-names specifies exactly 3 items.
How does this interact with variants that only have 2 interrupts?
> +
> + "#address-cells":
> + const: 1
> +
> + "#size-cells":
> + const: 0
> +
> + microchip,enable-anti-parallel:
> + description:
> + Enable anti-parallel diode mode operation.
> + MCP9984/84D/85/85D and MCP9933/33D support reading two external diodes
> + in anti-parallel connection on the same set of pins.
> + type: boolean
> +
> + microchip,parasitic-res-on-channel1-2:
> + description:
> + Indicates that the chip and the diodes/transistors are sufficiently far
> + apart that a parasitic resistance is added to the wires, which can affect
> + the measurements. Due to the anti-parallel diode connections, channels
> + 1 and 2 are affected together.
> + type: boolean
> +
> + microchip,parasitic-res-on-channel3-4:
> + description:
> + Indicates that the chip and the diodes/transistors are sufficiently far
> + apart that a parasitic resistance is added to the wires, which can affect
> + the measurements. Due to the anti-parallel diode connections, channels
> + 3 and 4 are affected together.
> + type: boolean
> +
> + microchip,power-state:
> + description:
> + The chip can be set in Run state or Standby state. In Run state the ADC
> + is converting on all channels at the programmed conversion rate.
> + In Standby state the host must initiate a conversion cycle by writing
> + to the One-Shot register.
> + True value sets Run state.
> + Chips with "D" in the name can only be set in Run mode.
> + type: boolean
> +
> + vdd-supply: true
> +
> +patternProperties:
> + "^channel@[1-4]$":
> + description:
> + Represents the external temperature channels to which
> + a remote diode is connected.
> + type: object
> +
> + properties:
> + reg:
> + items:
> + minItems: 1
> + maxItems: 4
Should the reg property in a channel node allow up to 4 items? Since the
node naming ^channel@[1-4]$ implies a single channel per node, it seems
reg should have maxItems: 1.
Second feedback:
Is this reg schema correct? For a single cell index (e.g. reg = <1>), the
items are integers, and minItems/maxItems are not valid constraints on
integers. Did you mean to use minimum/maximum here, or just maxItems: 1
on the reg itself?
> +
> + label:
> + description: Unique name to identify which channel this is.
> +
> + required:
> + - reg
> +
> + additionalProperties: false
> +
> +required:
> + - compatible
> + - reg
> + - vdd-supply
> +
> +allOf:
> + - if:
> + properties:
> + compatible:
> + contains:
> + enum:
> + - microchip,mcp9982d
> + - microchip,mcp9983d
> + - microchip,mcp9984d
> + - microchip,mcp9985d
> + - microchip,mcp9933d
> + then:
> + properties:
> + interrupts-names:
Is "interrupts-names" a typo for "interrupt-names"? The plural form
does not match the property defined at the top level.
Also, if the top-level interrupt-names requires 3 items, will a 2-item
override here conflict during validation?
> + items:
> + - const: alert-therm
> + - const: sys-shutdown
> + required:
> + - microchip,power-state
> + else:
> + properties:
> + interrupts-names:
Same question here regarding the typo; should this be interrupt-names?
> + items:
> + - const: alert-therm
> + - const: therm-addr
> + microchip,power-state: true
> +
> + - if:
> + properties:
> + compatible:
> + contains:
> + pattern: '^microchip,mcp998(2|3)$'
> + then:
> + properties:
> + microchip,enable-anti-parallel: false
If "D" variants only support Run mode as described in the property
description, why is this property required in the devicetree?
Second feedback:
Since the description says "D" versions can only be set in Run mode
(where True sets Run state), should this property also have a const: true
constraint here?
> +
> + - if:
> + properties:
> + compatible:
> + contains:
> + pattern: '^microchip,mcp998(2|3)d$'
> + then:
> + properties:
> + microchip,enable-anti-parallel: false
> + required:
> + - microchip,parasitic-res-on-channel1-2
> + - microchip,parasitic-res-on-channel3-4
Should the parasitic resistance compensation properties be required? These
represent board-specific parasitics and may not be present on all
designs using these chip variants.
> +
> + - if:
> + properties:
> + compatible:
> + contains:
> + pattern: '^microchip,mcp99(33|8[4-5])d$'
> + then:
> + required:
> + - microchip,parasitic-res-on-channel1-2
> + - microchip,parasitic-res-on-channel3-4
> +
> +additionalProperties: false
> +
> +examples:
> + - |
> + i2c {
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + temperature-sensor@4c {
> + compatible = "microchip,mcp9985";
> + reg = <0x4c>;
> +
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + microchip,enable-anti-parallel;
> + microchip,parasitic-res-on-channel1-2;
> + microchip,parasitic-res-on-channel3-4;
> +
> + vdd-supply = <&vdd>;
> +
> + channel@1 {
> + reg = <1>;
> + label = "Room Temperature";
> + };
> +
> + channel@2 {
> + reg = <2>;
> + label = "GPU Temperature";
> + };
> + };
> + };
> +
> +...
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 0d044a58cbfe..f88d837cb586 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -17149,6 +17149,12 @@ S: Maintained
> F: Documentation/devicetree/bindings/iio/adc/microchip,mcp3911.yaml
> F: drivers/iio/adc/mcp3911.c
>
> +MICROCHIP MCP9982 TEMPERATURE DRIVER
> +M: Victor Duicu <victor.duicu@...rochip.com>
> +L: linux-hwmon@...r.kernel.org
> +S: Supported
> +F: Documentation/devicetree/bindings/hwmon/microchip,mcp9982.yaml
> +
> MICROCHIP MMC/SD/SDIO MCI DRIVER
> M: Aubin Constans <aubin.constans@...rochip.com>
> S: Maintained
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