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Message-ID: <d6c318bed4a2e61ffaac556ba1073e91c1307902.camel@microchip.com>
Date: Mon, 28 Jul 2025 13:01:04 +0000
From: <Victor.Duicu@...rochip.com>
To: <robh@...nel.org>, <krzk+dt@...nel.org>, <jic23@...nel.org>,
<nuno.sa@...log.com>, <dlechner@...libre.com>, <conor+dt@...nel.org>,
<andy@...nel.org>
CC: <Marius.Cristea@...rochip.com>, <devicetree@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <linux-iio@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] dt-bindings: iio: temperature: add support for
MCP998X
Hi everyone,
I am writing this message to ask your opinions regarding the placement
of temperature range property from the MCP998X/XD family in the
devicetree.
The reason why I am bringing back this topic is due to a limitation of
the chips. When the moving average filter is enabled, the old readings
are kept and new readings are added to the average. This is a problem
when changing the range of temperatures. The raw temperature values
change based on the range so the mixed values will give erroneous
results during averaging.
One possible workaround for this behavior is to set the temperature
range before runtime, to not allow the user to change it.
Initially, in the first patch, I have placed the property
microchip,extended-temp-range in the devicetree.
At that point I mistakenly did not include Conor, Krzysztof and Rob in
the discussion and I would like to ask for comments.
Below is the discussion between me and Jonathan from patch v1:
> > > > +
> > > > + microchip,extended-temp-range:
> > > > + description: |
> > > > + Set the chip to work in the extended temperature range
> > > > -64
> > > > degrees C to 191.875 degrees C.
> > > > + Omit this tag to set the default range 0 degrees C to
> > > > 127.875 degrees C
> > > > + type: boolean
> > >
> > > I'm curious. Why does this belong in the DT binding?
> > >
> >
> > Regarding microchip,extended-temp-range, my perspective is that the
> > user knows beforehand which specific range of temperatures he
> > needs.
> > For example, if the device to be measured is a freezer, the user
> > would
> > be interested in temperatures below 0 degrees C. If we monitor a
> > CPU,
> > the user would be interested in temperatures above 0 degrees C.
>
> Maybe - though also easy to control from userspace by making the
> offset writeable.
Thank you,
Victor Duicu
On Fri, 2025-06-13 at 16:02 +0300, victor.duicu@...rochip.com wrote:
> From: Victor Duicu <victor.duicu@...rochip.com>
>
> This is the devicetree schema for Microchip MCP998X/33 and
> MCP998XD/33D Automotive Temperature Monitor Family.
>
> Signed-off-by: Victor Duicu <victor.duicu@...rochip.com>
> ---
> .../iio/temperature/microchip,mcp9982.yaml | 211
> ++++++++++++++++++
> 1 file changed, 211 insertions(+)
> create mode 100644
> Documentation/devicetree/bindings/iio/temperature/microchip,mcp9982.y
> aml
>
> diff --git
> a/Documentation/devicetree/bindings/iio/temperature/microchip,mcp9982
> .yaml
> b/Documentation/devicetree/bindings/iio/temperature/microchip,mcp9982
> .yaml
> new file mode 100644
> index 000000000000..ec939d463612
> --- /dev/null
> +++
> b/Documentation/devicetree/bindings/iio/temperature/microchip,mcp9982
> .yaml
> @@ -0,0 +1,211 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id:
> http://devicetree.org/schemas/iio/temperature/microchip,mcp9982.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Microchip MCP998X/33 and MCP998XD/33D Multichannel Automotive
> + Temperature Monitor Family
> +
> +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:
> + minItems: 2
> + maxItems: 2
> +
> + interrupt-names:
> + description:
> + -alert-therm is used to handle a HIGH or LOW limit.
> + -therm-addr is used to handle a THERM limit on chips
> + without "D" in the name.
> + -sys-shutdown is used to handle a THERM limit on chips
> + with "D" in the name.
> + items:
> + - const: alert-therm
> + - const: therm-addr
> + - const: sys-shutdown
> +
> + "#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,beta1:
> + description:
> + Set beta compensation value for external channel 1.
> + <0> 0.050
> + <1> 0.066
> + <2> 0.087
> + <3> 0.114
> + <4> 0.150
> + <5> 0.197
> + <6> 0.260
> + <7> 0.342
> + <8> 0.449
> + <9> 0.591
> + <10> 0.778
> + <11> 1.024
> + <12> 1.348
> + <13> 1.773
> + <14> 2.333
> + <15> Diode_Mode
> + <16> Auto
> + - Diode_Mode is used when measuring a discrete thermal diode
> + or a CPU diode that functions like a discrete thermal diode.
> + - Auto enables beta auto-detection. The chip monitors
> + external diode/transistor and determines the optimum
> + setting.
> + $ref: /schemas/types.yaml#/definitions/uint32
> + default: 16
> +
> + microchip,beta2:
> + description:
> + Set beta compensation value for external channel 2.
> + $ref: /schemas/types.yaml#/definitions/uint32
> + default: 16
> +
> + microchip,resistance-comp-ch1-2-enable:
> + description:
> + Enable resistance error correction(REC) for external channels
> 1 and 2.
> + The chip internal hardware counterbalances the parasitic
> resistance in
> + series with the external diodes. The compensation can be
> activated or
> + disabled in hardware for both channels 1 and 2 at the same
> time.
> + type: boolean
> +
> + microchip,resistance-comp-ch3-4-enable:
> + description:
> + Enable resistance error correction(REC) for external channels
> 3 and 4.
> + The chip internal hardware counterbalances the parasitic
> resistance in
> + series with the external diodes. The compensation can be
> activated or
> + disabled in hardware for both channels 3 and 4 at the same
> time.
> + type: boolean
> +
> +
> + vdd-supply: true
> +
> +patternProperties:
> + "^channel@[1-4]$":
> + description:
> + Represents the external temperature channels to which
> + a remote diode is connected.
> + type: object
> +
> + properties:
> + reg:
> + items:
> + minimum: 1
> + maximum: 4
> +
> + microchip,ideality-factor:
> + description:
> + Each channel has an ideality factor.
> + Beta compensation and resistance error correction
> automatically
> + correct for most ideality errors. So ideality factor does
> not need
> + to be adjusted in general.
> + $ref: /schemas/types.yaml#/definitions/uint32
> + default: 18
> +
> + 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:
> + items:
> + - const: alert-therm
> + - const: sys-shutdown
> + else:
> + properties:
> + interrupts-names:
> + items:
> + - const: alert-therm
> + - const: therm-addr
> +
> +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,resistance-comp-ch1-2-enable;
> + microchip,resistance-comp-ch3-4-enable;
> + microchip,beta1 = <16>;
> + microchip,beta2 = <16>;
> + vdd-supply = <&vdd>;
> +
> + channel@1 {
> + reg = <1>;
> + label = "CPU Temperature";
> + };
> +
> + channel@2 {
> + reg = <2>;
> + label = "GPU Temperature";
> + };
> + };
> + };
> +
> +...
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