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Thu, 23 Sep 2021 17:29:52 -0700 (PDT) Sender: Guenter Roeck Date: Thu, 23 Sep 2021 17:29:51 -0700 From: Guenter Roeck To: Rob Herring Cc: Krzysztof Adamski , Jean Delvare , Linux HWMON List , devicetree@vger.kernel.org, Oskar Senft Subject: Re: [PATCH 8/8] dt-bindings: hwmon: allow specifying channels for tmp421 Message-ID: <20210924002951.GA3027924@roeck-us.net> References: <12984255aac11a3edfc0e6278e1a1cac70ce97ec.1631021349.git.krzysztof.adamski@nokia.com> <20210921125831.GB1864238@roeck-us.net> <20210921205247.GA2363535@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Thu, Sep 23, 2021 at 10:30:59AM -0500, Rob Herring wrote: > On Tue, Sep 21, 2021 at 3:52 PM Guenter Roeck wrote: > > > > On Tue, Sep 21, 2021 at 02:06:18PM -0500, Rob Herring wrote: > > > On Tue, Sep 21, 2021 at 7:58 AM Guenter Roeck wrote: > > > > > > > > On Mon, Sep 20, 2021 at 05:24:09PM -0500, Rob Herring wrote: > > > > > On Tue, Sep 07, 2021 at 03:46:14PM +0200, Krzysztof Adamski wrote: > > > > > > Add binding description for the per temperature channel configuration > > > > > > like labels and n-factor. > > > > > > > > > > > > Signed-off-by: Krzysztof Adamski > > > > > > --- > > > > > > .../devicetree/bindings/hwmon/tmp421.yaml | 66 +++++++++++++++++++ > > > > > > 1 file changed, 66 insertions(+) > > > > > > > > > > I'd keep this separate... > > > > > > > > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/hwmon/tmp421.yaml b/Documentation/devicetree/bindings/hwmon/tmp421.yaml > > > > > > index 53940e146ee6..56085fdf1b57 100644 > > > > > > --- a/Documentation/devicetree/bindings/hwmon/tmp421.yaml > > > > > > +++ b/Documentation/devicetree/bindings/hwmon/tmp421.yaml > > > > > > @@ -24,12 +24,49 @@ properties: > > > > > > reg: > > > > > > maxItems: 1 > > > > > > > > > > > > + '#address-cells': > > > > > > + const: 1 > > > > > > + > > > > > > + '#size-cells': > > > > > > + const: 0 > > > > > > + > > > > > > required: > > > > > > - compatible > > > > > > - reg > > > > > > > > > > > > additionalProperties: false > > > > > > > > > > > > +patternProperties: > > > > > > + "^input@([0-4])$": > > > > > > + type: object > > > > > > + description: | > > > > > > + Represents channels of the device and their specific configuration. > > > > > > + > > > > > > + properties: > > > > > > + reg: > > > > > > + description: | > > > > > > + The channel number. 0 is local channel, 1-4 are remote channels > > > > > > + items: > > > > > > + minimum: 0 > > > > > > + maximum: 4 > > > > > > + > > > > > > + label: > > > > > > + description: | > > > > > > + A descriptive name for this channel, like "ambient" or "psu". > > > > > > + > > > > > > + n-factor: > > > > > > > > > > ti,n-factor > > > > > > > > n-factor isn't just supported by TI sensors, though it isn't always called > > > > n-factor. Maxim (eg MAX6581) uses the term "ideality factor", though they > > > > also refer to the factor as "N" in the datasheet. > > > > > > > > So question is if we make this ti,n-factor and maxim,n-factor, or if we make > > > > it generic and define some kind of generic units. Thoughts ? My personal > > > > preference would be a generic definition, but is not a strong preference. > > > > > > generic if the units are generic. Though if the register value is > > > opaque to s/w, then maybe register value is fine. > > > > > > > In regard to units, the n-factor is, as the name says, a factor. Default > > > > value is 1.008. The value range for MAX6581 is 0.999 to 1.030. For TMP421 > > > > it is 0.706542 to 1.747977. So the scondary question is if the value > > > > written should be the register value (as proposed here) or the absolute > > > > factor (eg in micro-units). > > > > > > A range, but the register value can only be 0 or 1? > > > > > No, register values are 0x0 .. 0x1f for MAX6581, and 0x0 .. 0xff for TMP421. > > Okay, then the schema below is wrong. > > > > > > Needs a type reference too. > > > > > > > > > > > + description: | > > > > > > + The value (two's complement) to be programmed in the channel specific N correction register. > > > > > > + For remote channels only. > > > > > > + items: > > > > > > + minimum: 0 > > > > > > + maximum: 1 > > > > > > + > > > > > > + required: > > > > > > + - reg > > > > > > + > > > > > > + additionalProperties: false > > > > > > + > > > > > > examples: > > > > > > - | > > > > > > i2c { > > > > > > @@ -41,3 +78,32 @@ examples: > > > > > > reg = <0x4c>; > > > > > > }; > > > > > > }; > > > > > > + - | > > > > > > + i2c { > > > > > > + #address-cells = <1>; > > > > > > + #size-cells = <0>; > > > > > > + > > > > > > + sensor@4c { > > > > > > + compatible = "ti,tmp422"; > > > > > > + reg = <0x4c>; > > > > > > + #address-cells = <1>; > > > > > > + #size-cells = <0>; > > > > > > + > > > > > > + input@0 { > > > > > > + reg = <0x0>; > > > > > > + n-factor = <0x1>; > > > > > > + label = "local"; > > > > > > + }; > > > > > > > > In the context or other sensors, question here is if we can make the > > > > bindings generic. We have been discussing this for NCT7802Y. The main > > > > question for me is how to handle different sensor types. TMP421 is > > > > easy because it only has one type of sensors, but there are other > > > > devices which also have, for example, voltage and/or current sensors. > > > > NCT7802 is an example for that. We just had a set of bindings for that > > > > chip proposed at > > > > https://patchwork.kernel.org/project/linux-hwmon/patch/20210921004627.2786132-1-osk@google.com/ > > > > > > > > Would it be possible to determine a generic scheme that works for all > > > > chips ? I can see two problems: > > > > - How to express sensor types. The NCT7802 submission proposes another level > > > > of indirection, ie > > > > > > > > temperature-sensors { > > > > > > + > > > > > > + input@1 { > > > > > > + reg = <0x1>; > > > > > > + n-factor = <0x0>; > > > > > > + label = "somelabel"; > > > > > > + }; > > > > > > + > > > > > > + input@2 { > > > > > > + reg = <0x2>; > > > > > > + status = "disabled"; > > > > > > + }; > > > > > > + }; > > > > > > + }; > > > > }; > > > > > > I think the function should be within the node. Otherwise, the > > > addressing becomes weird (e.g. input@3 is under current-sensors or > > > something) with seemingly separate address spaces. > > > > > > > Sorry, can you translate that for a DT non-expert ? Or, in other words, > > how would / should one express a chip with sets of, say, current-sensors, > > voltage sensors, and temperature sensors. Each would have a different > > number of channels and different parameters. > > If each kind of sensor is a different number space (e.g. 0-2), then > how you have it with 2 levels of nodes is appropriate. If you only > have one set of channel or input numbers, then they should all have > the same parent node. So is it current sensors 0,1,2 and temperature > sensors 0,1,2, or just input channels 0,1,2,3,4,5? > Each sensor type has its own number space. > > > > The second question is how to express sensor index. One option is the solution > > > > suggested here, ie to use reg=<> as sensor index. The second is the solution > > > > suggested in the 7802 bindings, where the (chip specific) name is used as > > > > sensor index. > > > > > > > > + temperature-sensors { > > > > + ltd { > > > > + status = "disabled"; > > > > + }; > > > > + > > > > + rtd1 { > > > > + status = "okay"; > > > > + type = <4> /* thermistor */; > > > > > > 'type' is a bit generic. We don't want the same property name to > > > possibly have multiple definitions. > > > > > How about sensor-type ? > > Sure. And you are going to define a common set of type numbers? > I guess we would have to. Guenter