On Sun, 16 May 2021 08:54:06 -0700 Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > On 5/16/21 8:02 AM, Liam Beguin wrote: > > Hi Jonathan, > > > > On Sun May 16, 2021 at 5:06 AM EDT, Jonathan Cameron wrote: > >> On Sun, 16 May 2021 00:43:13 -0400 > >> Liam Beguin <liambeguin@xxxxxxxxx> wrote: > >> > >>> Add a devicetree binding to optionally force a different IIO channel > >>> type. > >>> > >>> This is useful in cases where ADC channels are connected to a circuit > >>> that represent another unit such as a temperature or a current. > >>> > >>> `channel-types` was chosen instead of `io-channel-types` as this is not > >>> part of the iio consumer bindings. > >>> > >>> In the current form, this patch does what it's intended to do: > >>> change the unit displayed by `sensors`, but feels like the wrong way to > >>> address the problem. > >>> > >>> Would it be possible to force the type of different IIO channels for > >>> this kind of use case with a devicetree binding from the IIO subsystem? > >>> > >>> It would be convenient to do it within the IIO subsystem to have the > >>> right unit there too. > >>> > >>> Thanks for your time, > >>> Liam > >> > >> Hi Liam, > >> > >> +CC Peter for AFE part. > >> > >> It's an interesting approach, but I would suggest we think about this > >> a different way. > >> > >> Whenever a channel is being used to measure something 'different' from > >> what it actually measures (e.g. a voltage ADC measuring a current) that > >> reflects their being some analog component involved. > >> If you look at drivers/iio/afe/iio-rescale.c you can see the approach > >> we currently use to handle this. > > > > Many thanks for pointing out the AFE code. That look like what I was > > hoping to accomplish, but in a much better way. > > > >> > >> Effectively what you add to devicetree is a consumer of the ADC channel > >> which in turn provides services to other devices. For this current case > >> it would be either a current-sense-amplifier or a current-sense-shunt > >> depending on what the analog front end looks like. We have to describe > >> the characteristics of that front end which isn't something that can > >> be done via a simple channel type. > >> > > > > Understood. My original intention was to use sensors.conf to do the > > conversions and take into accounts those parameters. > > > >> That afe consumer device can then provide services to another consumer > >> (e.g. iio-hwmon) which work for your usecase. > >> > >> The main limitation of this approach currently is you end up with > >> one device per channel. That could be improved upon if you have a > >> usecase > >> where it matters. > >> > >> I don't think we currently have an equivalent for temperature sensing > >> but it would be easy enough to do something similar. > > > > Wonderful, thanks again for pointing out the AFE! > > > > Please don't reinvent the ntc_thermistor driver. Agreed, I'd forgotten it existed :( Had a feeling we'd solved that problem before but couldn't remember the name of the driver. The afe driver already deals with current / voltage scaling and conversion for common analog circuits. Potential dividers, current shunts etc, but they are all the linear cases IIRC. ntc_thermistor deals with the much more complex job of dealing with a thermistor. Thanks, Jonathan > > Thanks, > Guenter > > > Liam > > > >> > >> Jonathan > >> > >> > >>> > >>> Liam Beguin (2): > >>> hwmon: (iio_hwmon) optionally force iio channel type > >>> dt-bindings: hwmon: add iio-hwmon bindings > >>> > >>> .../devicetree/bindings/hwmon/iio-hwmon.yaml | 41 +++++++++++++++++++ > >>> drivers/hwmon/iio_hwmon.c | 2 + > >>> 2 files changed, 43 insertions(+) > >>> create mode 100644 Documentation/devicetree/bindings/hwmon/iio-hwmon.yaml > >>> > >>> > >>> base-commit: 9f4ad9e425a1d3b6a34617b8ea226d56a119a717 > > >
