From patchwork Sat Jan 8 20:53:19 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Liam Beguin X-Patchwork-Id: 12707628 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DCF97C4332F for ; Sat, 8 Jan 2022 20:54:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233007AbiAHUyO (ORCPT ); Sat, 8 Jan 2022 15:54:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50916 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233171AbiAHUx6 (ORCPT ); Sat, 8 Jan 2022 15:53:58 -0500 Received: from mail-qt1-x829.google.com (mail-qt1-x829.google.com [IPv6:2607:f8b0:4864:20::829]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0F770C061763; Sat, 8 Jan 2022 12:53:53 -0800 (PST) Received: by mail-qt1-x829.google.com with SMTP id bp39so9570624qtb.6; Sat, 08 Jan 2022 12:53:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=1iY9Z6nxGuMrblVO4UQYMXVHJL6H5huSq3eeUbaBoIY=; b=m4OsGMd/UUpI/hzhFvRhmejWMAe330FeHORHkKnNdXejyL7pKY0hzKalTaxP1Ah1Od YI/ncXbVChN3DZYDEAPXICS4eWv5yiIOUYi3ZGHMxYxEPjoi+9pmReJduhoaO8HDNCru 7WUXkOyrYeRvV6EM3fvDZeBx6EFPA2c9qlMBHB6jyE8RVi9BzFMANDVXLvE2t6NGQYtB cmFmN8yDQ+X+qGWARBMzpBy68DOlicmIYY4AdPBKTPaI9lscy3kN9HQPpoLPaAEbL6Wn vcsDenX37jqmJW7mt5MsyOHrUamLJMkC5LW7w5NRIDXBV7s1jVjk1nm7Gr/tRdWdirko Bg2A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=1iY9Z6nxGuMrblVO4UQYMXVHJL6H5huSq3eeUbaBoIY=; b=oXlcTU7zBZ1eQ6B1UJYQ9EftRBgNlZuQVa+2/0cqNLSsC5RGE4YTMw3Q42xLtGgv34 AdXZAmHBMa6ak8qFo/pzZZYuCHUhYzo63JuF/QCikQ/qCxmLzSv5wiHHuzS5b6uyXSRV ZJ6fFXWOpOwzMmLIG0pFW9FWNp5wgYYeP3hdwcK6szvqZONd0Cc8v6dfqYQ+PrS+zNAk o3K8woXjkL6LQoRxJ3ZadYEeJMaKh462vTqtEyEQR0dzS1Hlwjjiuku5ejTbh2g8DEfa 0ukMtC6aFrmdXMHeZEwKZz020wN5eJfVoiYfcBnG3V88V+3Nv+HQFOeNwzjM6ECOoY1/ 0Nbg== X-Gm-Message-State: AOAM533TYJPlqjmOXogCtV7RuHYdLnGx85xgkYIR1b1bEEthDoT6Ku0d V51hyw5bFUUqqJeuKvS4Lj8= X-Google-Smtp-Source: ABdhPJw8W9zSUtuQ9Yn7T8AGM60e9YkZH1RAD8IHFtS5SSRM53FS4tAAf/YxXwBvAnwZZk5Jg1fYlA== X-Received: by 2002:a05:622a:1713:: with SMTP id h19mr61036653qtk.464.1641675232255; Sat, 08 Jan 2022 12:53:52 -0800 (PST) Received: from shaak.. (69-165-204-82.cable.teksavvy.com. [69.165.204.82]) by smtp.gmail.com with ESMTPSA id p16sm1650377qtx.19.2022.01.08.12.53.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 08 Jan 2022 12:53:51 -0800 (PST) From: Liam Beguin To: liambeguin@gmail.com, peda@axentia.se, jic23@kernel.org, andy.shevchenko@gmail.com, lars@metafoo.de Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, devicetree@vger.kernel.org, robh+dt@kernel.org Subject: [PATCH v12 16/16] dt-bindings: iio: afe: add bindings for temperature transducers Date: Sat, 8 Jan 2022 15:53:19 -0500 Message-Id: <20220108205319.2046348-17-liambeguin@gmail.com> X-Mailer: git-send-email 2.34.0 In-Reply-To: <20220108205319.2046348-1-liambeguin@gmail.com> References: <20220108205319.2046348-1-liambeguin@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org An ADC is often used to measure other quantities indirectly. This binding describe one case, the measurement of a temperature through a temperature transducer (either voltage or current). Signed-off-by: Liam Beguin Reviewed-by: Rob Herring Reviewed-by: Peter Rosin --- .../iio/afe/temperature-transducer.yaml | 114 ++++++++++++++++++ 1 file changed, 114 insertions(+) create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml new file mode 100644 index 000000000000..cfbf5350db27 --- /dev/null +++ b/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml @@ -0,0 +1,114 @@ +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/iio/afe/temperature-transducer.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml# + +title: Temperature Transducer + +maintainers: + - Liam Beguin + +description: | + A temperature transducer is a device that converts a thermal quantity + into any other physical quantity. This binding applies to temperature to + voltage (like the LTC2997), and temperature to current (like the AD590) + linear transducers. + In both cases these are assumed to be connected to a voltage ADC. + + When an io-channel measures the output voltage of a temperature analog front + end such as a temperature transducer, the interesting measurement is almost + always the corresponding temperature, not the voltage output. This binding + describes such a circuit. + + The general transfer function here is (using SI units) + V(T) = Rsense * Isense(T) + T = (Isense(T) / alpha) + offset + T = 1 / (Rsense * alpha) * (V + offset * Rsense * alpha) + + When using a temperature to voltage transducer, Rsense is set to 1. + + The following circuits show a temperature to current and a temperature to + voltage transducer that can be used with this binding. + + VCC + ----- + | + +---+---+ + | AD590 | VCC + +---+---+ ----- + | | + V proportional to T +----+----+ + | D+ --+ | + +---- Vout | LTC2997 +--- Vout + | D- --+ | + +---+----+ +---------+ + | Rsense | | + +---+----+ ----- + | GND + ----- + GND + +properties: + compatible: + const: temperature-transducer + + io-channels: + maxItems: 1 + description: | + Channel node of a voltage io-channel. + + '#io-channel-cells': + const: 0 + + sense-offset-millicelsius: + description: | + Temperature offset. + This offset is commonly used to convert from Kelvins to degrees Celsius. + In that case, sense-offset-millicelsius would be set to <(-273150)>. + default: 0 + + sense-resistor-ohms: + description: | + The sense resistor. + By default sense-resistor-ohms cancels out the resistor making the + circuit behave like a temperature transducer. + default: 1 + + alpha-ppm-per-celsius: + description: | + Sometimes referred to as output gain, slope, or temperature coefficient. + + alpha is expressed in parts per million which can be micro-amps per + degrees Celsius or micro-volts per degrees Celsius. The is the main + characteristic of a temperature transducer and should be stated in the + datasheet. + +additionalProperties: false + +required: + - compatible + - io-channels + - alpha-ppm-per-celsius + +examples: + - | + ad950: temperature-sensor-0 { + compatible = "temperature-transducer"; + #io-channel-cells = <0>; + io-channels = <&temp_adc 3>; + + sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */ + sense-resistor-ohms = <8060>; + alpha-ppm-per-celsius = <1>; /* 1 uA/K */ + }; + - | + znq_tmp: temperature-sensor-1 { + compatible = "temperature-transducer"; + #io-channel-cells = <0>; + io-channels = <&temp_adc 2>; + + sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */ + alpha-ppm-per-celsius = <4000>; /* 4 mV/K */ + }; +...