On Mon, 29 Mar 2021 15:06:20 +0200 Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> wrote: > On Mon, Mar 29, 2021 at 11:25:32AM +0100, Jonathan Cameron wrote: > > On Mon, 29 Mar 2021 09:31:29 +0200 > > Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> wrote: > > > > > Settling time and over sampling is a typical challenge for different IIO ADC > > > devices. So, introduce channel specific settling-time-us and oversampling-ratio > > > properties to cover this use case. > > > > > > Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> > > > --- > > > Documentation/devicetree/bindings/iio/adc/adc.yaml | 8 ++++++++ > > > 1 file changed, 8 insertions(+) > > > > > > diff --git a/Documentation/devicetree/bindings/iio/adc/adc.yaml b/Documentation/devicetree/bindings/iio/adc/adc.yaml > > > index 912a7635edc4..d5bc86d2a2af 100644 > > > --- a/Documentation/devicetree/bindings/iio/adc/adc.yaml > > > +++ b/Documentation/devicetree/bindings/iio/adc/adc.yaml > > > @@ -39,4 +39,12 @@ properties: > > > The first value specifies the positive input pin, the second > > > specifies the negative input pin. > > > > > > + settling-time-us: > > > + description: > > > + Time between enabling the channel and firs stable readings. > > > > first > > ack > > > > + > > > + oversampling-ratio: > > > + $ref: /schemas/types.yaml#/definitions/uint32 > > > + description: Number of data samples which are averaged for each read. > > > > I think I've asked about this in previous reviews, but I want a clear statement > > of why you think this property is a feature of the 'board' (and hence should be > > in device tree) rather than setting sensible defaults and leaving any control > > to userspace? > > yes, my reply was: Ah. I missed it somewhere along the way, thanks for repeating here. > > Oversampling is used as replacement of or addition to the low-pass filter. The > > filter can be implemented on board, but it will change settling time > > characteristic. Since low-pass filter is board specific characteristic, this > > property belongs in device tree as well. > > I could imagine that this values can be overwritten from user space for > diagnostic, but we need some working default values. Hmm. So low pass filters are interesting whether they are actually a characteristic of the board (obviously they are if they are resistors/ caps etc on the board), or of the application. Some applications want noisy messy data, others not so much. What filter you need to achieve a specific noise level on a given board is indeed a characteristic of the board. However, what that noise level is (which actually drives the decision) is not a board characteristic. If we have a configurable filter, then that can be argued to be a policy decision and hence userspace, not DT. > > Should I integrate this comment in to the yaml? Definitely. Whilst I'm not that keen on this one, you have made a reasonable argument that it is 'sort of' a board characteristic, so I can live with that as long as it is there. Perhaps the slightly amended version of the above. "Oversampling is used as replacement of or addition to the low-pass filter. In some cases, the desired filtering characteristics are a function the device design and can interact with other characteristics such as settling time." Jonathan > > Regards, > Oleksij
