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=-12.7 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,URIBL_BLOCKED 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 593EBC5519F for ; Wed, 18 Nov 2020 14:44:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CF31620825 for ; Wed, 18 Nov 2020 14:44:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Mli9DBt2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726274AbgKROnV (ORCPT ); Wed, 18 Nov 2020 09:43:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41074 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725446AbgKROnU (ORCPT ); Wed, 18 Nov 2020 09:43:20 -0500 Received: from mail-il1-x143.google.com (mail-il1-x143.google.com [IPv6:2607:f8b0:4864:20::143]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 45204C0613D4; Wed, 18 Nov 2020 06:43:19 -0800 (PST) Received: by mail-il1-x143.google.com with SMTP id t13so2204868ilp.2; Wed, 18 Nov 2020 06:43:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=XgVSIg8t9/+FM9rTxwtZKlIcvlhnQQH654LclswFZHo=; b=Mli9DBt2KISGsoDx0uXNKa6mWxqtzl26nVXiKIoFSaGdXiVyvkwOJ25sCP6d7sZRmc MK1RPWhY8eprSjrO2DvvF7OgLiZFGd1jNJzayZDWAVe0vynoe94K+hBee6uVHVi9ZRuE eiKV3Izo1L4t1c6V0ZZui6rOw04c/fpN9F7sCgI7oQuEkA3Gkld33CrLWQVMeKQ2vukh vM+K3I99mUQaKod1KlPUKxKgqZfSO+nvbel2YwVjkeUmDmqf0VtvEcmpytKe0vsiez8u 1NqhJ1JoU6bZgoiWZ7AIXajkDo4VlhDeQ1Ew4ji8JqkrMg5pLQmV5iiWaniqiH1767wC qbng== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=XgVSIg8t9/+FM9rTxwtZKlIcvlhnQQH654LclswFZHo=; b=sDZCyQbLMB/mM5nXHXmzy0/SyUnRpnIJqBWM1SQtO97wcAlK3s5dYZvEjmxIYgqWmI yzbvf/dci06skRXd9NL0RLPSHHcKenUp/kI9rE0kaHldIYOEp6W+gFqXutWfV/TNBf72 ukkDRmshoAU0NmQhL4wBvvxx1+ccV+OPxIJWvvtmmu8R3sCZ3JuEpmKZSwsHy7t6SEwl T3wLeuhVGKC/wO6jffvKosYHb09BFqk7YkTsREbxrImHUZ4+n9A4e07LqBWfJokW/lG8 S3JX2iCMzBinlCQBa7ERh/CScFb11zcnRfAsAsIG49dTkzBwh53k4WSlGJi4fBtSkNCM YTpg== X-Gm-Message-State: AOAM530QNWZmYrAlYuJe9bgqD2JkoLZEy1Exm1udZGeScX+lsXAeu8B6 jK6Kd3ik4XwRgsIGYLISiD38c50xxfd7diO98JM= X-Google-Smtp-Source: ABdhPJzI9KZsh5cYa1z3LoS4AewXMJXxwbVEAIO4qmVvtPNMIGF9H2MWMxsvY+ZfrqW6/RXLGgegg1dl9b4lDQwIExA= X-Received: by 2002:a92:c844:: with SMTP id b4mr16902080ilq.292.1605710598675; Wed, 18 Nov 2020 06:43:18 -0800 (PST) MIME-Version: 1.0 References: <20201111091259.46773-1-alexandru.ardelean@analog.com> <20201111091259.46773-4-alexandru.ardelean@analog.com> In-Reply-To: <20201111091259.46773-4-alexandru.ardelean@analog.com> From: Alexandru Ardelean Date: Wed, 18 Nov 2020 16:43:07 +0200 Message-ID: Subject: Re: [PATCH v2 3/4] hwmon: (ltc2945): add support for sense resistor To: Alexandru Ardelean Cc: linux-hwmon@vger.kernel.org, devicetree , LKML , Rob Herring , Guenter Roeck , jdelvare@suse.com, "Thoren, Mark" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org On Wed, Nov 11, 2020 at 11:08 AM Alexandru Ardelean wrote: > > The sense resistor is a parameter of the board. It should be configured in > the driver via a device-tree / ACPI property, so that the proper current > measurements can be done in the driver. > > It shouldn't be necessary that userspace need to know about the value of > the resistor. It makes things a bit harder to make the application code > portable from one board to another. > > This change implements support for the sense resistor to be configured from > DT/ACPI and used in current calculations. > > Signed-off-by: Alexandru Ardelean > --- > drivers/hwmon/ltc2945.c | 53 ++++++++++++++++++++--------------------- > 1 file changed, 26 insertions(+), 27 deletions(-) > > diff --git a/drivers/hwmon/ltc2945.c b/drivers/hwmon/ltc2945.c > index 6d4569a25471..909dd92a7a20 100644 > --- a/drivers/hwmon/ltc2945.c > +++ b/drivers/hwmon/ltc2945.c > @@ -61,9 +61,11 @@ > /** > * struct ltc2945_state - driver instance specific data > * @regmap regmap object to access device registers > + * @r_sense_uohm current sense resistor value > */ > struct ltc2945_state { > struct regmap *regmap; > + u32 r_sense_uohm; > }; > > static inline bool is_power_reg(u8 reg) > @@ -101,9 +103,8 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg) > case LTC2945_MAX_POWER_THRES_H: > case LTC2945_MIN_POWER_THRES_H: > /* > - * Convert to uW by assuming current is measured with > - * an 1mOhm sense resistor, similar to current > - * measurements. > + * Convert to uW by and scale it with the configured > + * sense resistor, similar to current measurements. > * Control register bit 0 selects if voltage at SENSE+/VDD > * or voltage at ADIN is used to measure power. > */ > @@ -112,10 +113,10 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg) > return ret; > if (control & CONTROL_MULT_SELECT) { > /* 25 mV * 25 uV = 0.625 uV resolution. */ > - val *= 625LL; > + val = DIV_ROUND_CLOSEST_ULL(val * 625LL * 1000, st->r_sense_uohm); > } else { > /* 0.5 mV * 25 uV = 0.0125 uV resolution. */ > - val = (val * 25LL) >> 1; > + val = DIV_ROUND_CLOSEST_ULL(val * 25LL * 1000, st->r_sense_uohm) >> 1; > } > break; > case LTC2945_VIN_H: > @@ -140,13 +141,10 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg) > case LTC2945_MAX_SENSE_THRES_H: > case LTC2945_MIN_SENSE_THRES_H: > /* > - * 25 uV resolution. Convert to current as measured with > - * an 1 mOhm sense resistor, in mA. If a different sense > - * resistor is installed, calculate the actual current by > - * dividing the reported current by the sense resistor value > - * in mOhm. > + * 25 uV resolution. Convert to current and scale it > + * with the value of the sense resistor. > */ > - val *= 25; > + val = DIV_ROUND_CLOSEST_ULL(val * 25 * 1000, st->r_sense_uohm); > break; > default: > return -EINVAL; > @@ -169,9 +167,8 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg, > case LTC2945_MAX_POWER_THRES_H: > case LTC2945_MIN_POWER_THRES_H: > /* > - * Convert to register value by assuming current is measured > - * with an 1mOhm sense resistor, similar to current > - * measurements. > + * Convert to register value, scale it with the configured sense > + * resistor value, similar to current measurements. > * Control register bit 0 selects if voltage at SENSE+/VDD > * or voltage at ADIN is used to measure power, which in turn > * determines register calculations. > @@ -181,14 +178,10 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg, > return ret; > if (control & CONTROL_MULT_SELECT) { > /* 25 mV * 25 uV = 0.625 uV resolution. */ > - val = DIV_ROUND_CLOSEST_ULL(val, 625); > + val = DIV_ROUND_CLOSEST_ULL(val * 1000, 625 * st->r_sense_uohm); I think that in this ltc2945_val_to_reg(), I should do the math the other way around. i.e. val = DIV_ROUND_CLOSEST_ULL(val * st->r_sense_uohm, 625000); I got confused initially and did it wrong. > } else { > - /* > - * 0.5 mV * 25 uV = 0.0125 uV resolution. > - * Divide first to avoid overflow; > - * accept loss of accuracy. > - */ > - val = DIV_ROUND_CLOSEST_ULL(val, 25) * 2; > + /* 0.5 mV * 25 uV = 0.0125 uV resolution. */ > + val = DIV_ROUND_CLOSEST_ULL(val * 2 * 1000, 25 * st->r_sense_uohm); > } > break; > case LTC2945_VIN_H: > @@ -213,13 +206,10 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg, > case LTC2945_MAX_SENSE_THRES_H: > case LTC2945_MIN_SENSE_THRES_H: > /* > - * 25 uV resolution. Convert to current as measured with > - * an 1 mOhm sense resistor, in mA. If a different sense > - * resistor is installed, calculate the actual current by > - * dividing the reported current by the sense resistor value > - * in mOhm. > + * 25 uV resolution. Convert to current and scale it > + * with the value of the sense resistor, in mA. > */ > - val = DIV_ROUND_CLOSEST_ULL(val, 25); > + val = DIV_ROUND_CLOSEST_ULL(val * 1000, 25 * st->r_sense_uohm); > break; > default: > return -EINVAL; > @@ -475,6 +465,15 @@ static int ltc2945_probe(struct i2c_client *client) > return PTR_ERR(regmap); > } > > + if (device_property_read_u32(dev, "shunt-resistor-micro-ohms", > + &st->r_sense_uohm)) > + st->r_sense_uohm = 1000; > + > + if (st->r_sense_uohm == 0) { > + dev_err(dev, "Zero value provided for sense resistor in DT"); > + return -EINVAL; > + } > + > st->regmap = regmap; > > /* Clear faults */ > -- > 2.17.1 >