From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.5 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 709F9C433E2 for ; Mon, 29 Mar 2021 15:21:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2725661996 for ; Mon, 29 Mar 2021 15:21:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230339AbhC2PVX (ORCPT ); Mon, 29 Mar 2021 11:21:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:54880 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229655AbhC2PVT (ORCPT ); Mon, 29 Mar 2021 11:21:19 -0400 Received: from jic23-huawei (cpc108967-cmbg20-2-0-cust86.5-4.cable.virginm.net [81.101.6.87]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2ECFD6187E; Mon, 29 Mar 2021 15:21:14 +0000 (UTC) Date: Mon, 29 Mar 2021 16:21:21 +0100 From: Jonathan Cameron To: Oleksij Rempel Cc: Rob Herring , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Pengutronix Kernel Team , David Jander , Robin van der Gracht , linux-iio@vger.kernel.org, Lars-Peter Clausen , Peter Meerwald-Stadler , Dmitry Torokhov Subject: Re: [PATCH v5 1/3] dt-bindings:iio:adc: add generic settling-time-us and oversampling-ratio channel properties Message-ID: <20210329162121.5a302356@jic23-huawei> In-Reply-To: <20210329130620.utfdlgwzixrenqka@pengutronix.de> References: <20210329073131.1759-1-o.rempel@pengutronix.de> <20210329073131.1759-2-o.rempel@pengutronix.de> <20210329112532.174825d6@jic23-huawei> <20210329130620.utfdlgwzixrenqka@pengutronix.de> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 29 Mar 2021 15:06:20 +0200 Oleksij Rempel 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 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 > > > --- > > > 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