From patchwork Mon Nov 15 03:43:34 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Liam Beguin X-Patchwork-Id: 12618653 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A8B66C433EF for ; Mon, 15 Nov 2021 03:44:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9072A61B4D for ; Mon, 15 Nov 2021 03:44:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237063AbhKODrL (ORCPT ); Sun, 14 Nov 2021 22:47:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50838 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237005AbhKODqu (ORCPT ); Sun, 14 Nov 2021 22:46:50 -0500 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 7491FC061746; Sun, 14 Nov 2021 19:43:55 -0800 (PST) Received: by mail-qv1-xf2b.google.com with SMTP id s9so10445955qvk.12; Sun, 14 Nov 2021 19:43:55 -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=ULLabupwpKZ9q0uzoJvIF5vhkAHSbV+6NawrmKl86jU=; b=YPsPndXsufgMAjwX+0mAHSmIjffN/anUwJ2PTqrKhaKIqnIVPEysGRIwqPGhrxZgrK ikU90sS+216cYhdvp6X5YOIIBqnXbvnLDoJE602hIpoBmyJxXm0RBzJ1wn+vVZQlbrcZ egK/bcvJl2sVwM+cKludIBhTugpcTmhk7hq7KiQt9c5p4obN2k33TDbm70ZhOH7Xwk5n AQ4LZ+DmmrapBPd7sjsn9gnEbFaKPWEj8dWvAPFZi1PA9WMv4wLg8lOhChNehZe3aY8s kB911cNLhE8aNOpO3bXON852akTbEzWGHKWo4l/OcnvBtcuMn2HaIrCbE4AiHq6rj7PA OA3g== 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=ULLabupwpKZ9q0uzoJvIF5vhkAHSbV+6NawrmKl86jU=; b=7vIAHuc+AVxnltVnTSQWDtygYSmAmghWMGK1WA+CR2v35T4pnMP6kEI2ZHMfznJijb Upf9pbe/xzUf/1kJ8AGjoNzjNLsx4Ctp6STYp4cvPgsOVLGVfF2n56sZnuO/SaTYx4Dq P+rSzfF0vDYFU2KSNutWnRp98GTqJbHSxMgVqSBv/xcjYAvtl5lcbphayqNO+76Q/AdG E2vWfqmWeJVwutP7pgl9RuQgdexGh3xnlkTnUZkUyZqb1LXCrsd90qt7rte7E5hBBakO 2jX77krgos+faWxcP9ZaA9J7zUSbpv0B2CuE5aGvSb7kpWqkAhvX9BwIWvlRwPx9gmb4 W0DQ== X-Gm-Message-State: AOAM531PuCXBw//vpVRFiv9bZds/AjzdfwCZnEiZ0xoOgs+pz8cn6tfm W7EVveJyXYxEipWZg2TPhdSZF8FS6vw= X-Google-Smtp-Source: ABdhPJz3CT2phySirIRZCTcHO911TUPPF4oXibyT0E6xf2aW91lBsp6wLHXGreA/GGVzLdk4id+skQ== X-Received: by 2002:a0c:fa07:: with SMTP id q7mr34051205qvn.18.1636947834600; Sun, 14 Nov 2021 19:43:54 -0800 (PST) Received: from shaak.. (198-48-202-89.cpe.pppoe.ca. [198.48.202.89]) by smtp.gmail.com with ESMTPSA id h5sm206519qkn.62.2021.11.14.19.43.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Nov 2021 19:43:54 -0800 (PST) From: Liam Beguin To: liambeguin@gmail.com, peda@axentia.se, jic23@kernel.org, lars@metafoo.de Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, devicetree@vger.kernel.org, robh+dt@kernel.org Subject: [PATCH v9 14/14] dt-bindings: iio: afe: add bindings for temperature transducers Date: Sun, 14 Nov 2021 22:43:34 -0500 Message-Id: <20211115034334.1713050-15-liambeguin@gmail.com> X-Mailer: git-send-email 2.32.0.452.g940fe202adcb In-Reply-To: <20211115034334.1713050-1-liambeguin@gmail.com> References: <20211115034334.1713050-1-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 Reviewed-by: Rob Herring --- .../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 */ + }; +...