From patchwork Thu Jul 15 03:12:15 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Liam Beguin X-Patchwork-Id: 12378369 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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham 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 28008C1B08C for ; Thu, 15 Jul 2021 03:12:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 125B0613B4 for ; Thu, 15 Jul 2021 03:12:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233467AbhGODPu (ORCPT ); Wed, 14 Jul 2021 23:15:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233574AbhGODPl (ORCPT ); Wed, 14 Jul 2021 23:15:41 -0400 Received: from mail-qv1-xf2b.google.com (mail-qv1-xf2b.google.com [IPv6:2607:f8b0:4864:20::f2b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 96461C061764; Wed, 14 Jul 2021 20:12:47 -0700 (PDT) Received: by mail-qv1-xf2b.google.com with SMTP id i4so2148081qvq.10; Wed, 14 Jul 2021 20:12:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=aE1V8QRfi8n6sF30lMvTx95RKdAsIa59F0QLZHJ2zOc=; b=m0qFAw1m0kNwdNacHFNTF36k2HELiH8XJ81F8hZMnBvE0tR7vpIbe4pkRLhtVUuc4C QsuMbYCpXTCt20+yduDxtsb6nCKF1O5e+xu9OBgPR5WIGtzFsGKJ5td9I9T2YeD74suq F4g6zU0+1n2NdSEV4xJh+3PL0liOs3mSSkh2BCloqtCoQ0Ks9aXKYv9xf0YFoiIX5PE2 i5qkbIK1zOjet3p1e/1GbqchhsnHV/JLSGODIUu72dKpWZLjwJGTWvnJVzpnVaw9d+fm /Wmc9niXw+M5SX9ypa4rt/dQyB5RQzl92bZt/nuLFWIyt//0AROZA6sOWo/ILP792Yqt ILng== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=aE1V8QRfi8n6sF30lMvTx95RKdAsIa59F0QLZHJ2zOc=; b=KQsCDcMEggbE9gPQjgmZ2Ds+i5H61J0jMjcXmyu5zIYcpO4WswPQjWTK8t55dc8VWs M/aimTo6aY4fwQQE5XwnbKsk8um/O3Z+2k4cvJjJiS2i+HN+W1tupyX7R+kyvVR3EZox HcqLMWmC7I7kyj89hYQ3PJu7sz0V5pBsekInhPom3cq99yfjGjMT/fQNlH/lf30hY46I e+PZ8YcvDO/EOJcOA0OHmOa+8VJz6f0b7ILM3Rwi9GDBfYj1W8/4aYTYHxTYZBYCCG7b yYzJ4A/t0g9TSXJku7c+q/pGvPG7OG5d4P1m7aKcKFXGpaEEce1UfkGKv6iG9l97JZ9g UZNg== X-Gm-Message-State: AOAM533v33B1EL0xMaHk62w3dVS3SX86CW4napim4IbqCMcTcUY8FDjl mCRgCmUFV3rtx3R7f6qPRd4= X-Google-Smtp-Source: ABdhPJzqjXQ0AVrEApOwNga/whINVfmKLmbLmX3gNSLkmbXvS9XTMyqE7+miZ/AQ7v5MOeF2A3+Lbw== X-Received: by 2002:a0c:ea31:: with SMTP id t17mr1753088qvp.17.1626318766735; Wed, 14 Jul 2021 20:12:46 -0700 (PDT) Received: from shaak.. (198-48-202-89.cpe.pppoe.ca. [198.48.202.89]) by smtp.gmail.com with ESMTPSA id t125sm1932847qkf.41.2021.07.14.20.12.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Jul 2021 20:12:46 -0700 (PDT) From: Liam Beguin To: liambeguin@gmail.com, peda@axentia.se, jic23@kernel.org, lars@metafoo.de, pmeerw@pmeerw.net Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, devicetree@vger.kernel.org, robh+dt@kernel.org Subject: [PATCH v5 10/10] dt-bindings: iio: afe: add bindings for temperature transducers Date: Wed, 14 Jul 2021 23:12:15 -0400 Message-Id: <20210715031215.1534938-11-liambeguin@gmail.com> X-Mailer: git-send-email 2.30.1.489.g328c10930387 In-Reply-To: <20210715031215.1534938-1-liambeguin@gmail.com> References: <20210715031215.1534938-1-liambeguin@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org From: Liam Beguin 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 --- .../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..41411514aee0 --- /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 */ + }; +...