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Date: Wed, 28 Feb 2018 09:03:48 +0200
From: Mikko Perttunen <cyndis@...si.fi>
To: Rajkumar Rampelli <rrajk@...dia.com>,
Guenter Roeck <linux@...ck-us.net>, robh+dt@...nel.org,
mark.rutland@....com, thierry.reding@...il.com,
jonathanh@...dia.com, jdelvare@...e.com, corbet@....net,
catalin.marinas@....com, will.deacon@....com,
kstewart@...uxfoundation.org, gregkh@...uxfoundation.org,
pombredanne@...b.com, mmaddireddy@...dia.com,
mperttunen@...dia.com, arnd@...db.de, timur@...eaurora.org,
andy.gross@...aro.org, xuwei5@...ilicon.com, elder@...aro.org,
heiko@...ech.de, krzk@...nel.org, ard.biesheuvel@...aro.org
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-pwm@...r.kernel.org, linux-tegra@...r.kernel.org,
linux-hwmon@...r.kernel.org, linux-doc@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, ldewangan@...dia.com
Subject: Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM
based tachometer
On 02/28/2018 08:12 AM, Rajkumar Rampelli wrote:
>
> On Wednesday 28 February 2018 11:28 AM, Guenter Roeck wrote:
>> On 02/27/2018 09:38 PM, Rajkumar Rampelli wrote:
>>>
>>> On Wednesday 21 February 2018 08:20 PM, Guenter Roeck wrote:
>>>> On 02/20/2018 10:58 PM, Rajkumar Rampelli wrote:
>>>>> Add generic PWM based tachometer driver via HWMON interface
>>>>> to report the RPM of motor. This drivers get the period/duty
>>>>> cycle from PWM IP which captures the motor PWM output.
>>>>>
>>>>> This driver implements a simple interface for monitoring the speed of
>>>>> a fan and exposes it in roatations per minute (RPM) to the user space
>>>>> by using the hwmon's sysfs interface
>>>>>
>>>>> Signed-off-by: Rajkumar Rampelli <rrajk@...dia.com>
>>>>> ---
>>>>> Documentation/hwmon/generic-pwm-tachometer | 17 +++++
>>>>> drivers/hwmon/Kconfig | 10 +++
>>>>> drivers/hwmon/Makefile | 1 +
>>>>> drivers/hwmon/generic-pwm-tachometer.c | 112
>>>>> +++++++++++++++++++++++++++++
>>>>> 4 files changed, 140 insertions(+)
>>>>> create mode 100644 Documentation/hwmon/generic-pwm-tachometer
>>>>> create mode 100644 drivers/hwmon/generic-pwm-tachometer.c
>>>>>
>>>>> diff --git a/Documentation/hwmon/generic-pwm-tachometer
>>>>> b/Documentation/hwmon/generic-pwm-tachometer
>>>>> new file mode 100644
>>>>> index 0000000..e0713ee
>>>>> --- /dev/null
>>>>> +++ b/Documentation/hwmon/generic-pwm-tachometer
>>>>> @@ -0,0 +1,17 @@
>>>>> +Kernel driver generic-pwm-tachometer
>>>>> +====================================
>>>>> +
>>>>> +This driver enables the use of a PWM module to monitor a fan. It
>>>>> uses the
>>>>> +generic PWM interface and can be used on SoCs as along as the SoC
>>>>> supports
>>>>> +Tachometer controller that moniors the Fan speed in periods.
>>>>> +
>>>>> +Author: Rajkumar Rampelli <rrajk@...dia.com>
>>>>> +
>>>>> +Description
>>>>> +-----------
>>>>> +
>>>>> +The driver implements a simple interface for monitoring the Fan
>>>>> speed using
>>>>> +PWM module and Tachometer controller. It requests period value
>>>>> through PWM
>>>>> +capture interface to Tachometer and measures the Rotations per
>>>>> minute using
>>>>> +received period value. It exposes the Fan speed in RPM to the user
>>>>> space by
>>>>> +using the hwmon's sysfs interface.
>>>>> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
>>>>> index ef23553..8912dcb 100644
>>>>> --- a/drivers/hwmon/Kconfig
>>>>> +++ b/drivers/hwmon/Kconfig
>>>>> @@ -1878,6 +1878,16 @@ config SENSORS_XGENE
>>>>> If you say yes here you get support for the temperature
>>>>> and power sensors for APM X-Gene SoC.
>>>>> +config GENERIC_PWM_TACHOMETER
>>>>> + tristate "Generic PWM based tachometer driver"
>>>>> + depends on PWM
>>>>> + help
>>>>> + Enables a driver to use PWM signal from motor to use
>>>>> + for measuring the motor speed. The RPM is captured by
>>>>> + PWM modules which has PWM capture capability and this
>>>>> + drivers reads the captured data from PWM IP to convert
>>>>> + it to speed in RPM.
>>>>> +
>>>>> if ACPI
>>>>> comment "ACPI drivers"
>>>>> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
>>>>> index f814b4a..9dcc374 100644
>>>>> --- a/drivers/hwmon/Makefile
>>>>> +++ b/drivers/hwmon/Makefile
>>>>> @@ -175,6 +175,7 @@ obj-$(CONFIG_SENSORS_WM8350) += wm8350-hwmon.o
>>>>> obj-$(CONFIG_SENSORS_XGENE) += xgene-hwmon.o
>>>>> obj-$(CONFIG_PMBUS) += pmbus/
>>>>> +obj-$(CONFIG_GENERIC_PWM_TACHOMETER) += generic-pwm-tachometer.o
>>>>> ccflags-$(CONFIG_HWMON_DEBUG_CHIP) := -DDEBUG
>>>>> diff --git a/drivers/hwmon/generic-pwm-tachometer.c
>>>>> b/drivers/hwmon/generic-pwm-tachometer.c
>>>>> new file mode 100644
>>>>> index 0000000..9354d43
>>>>> --- /dev/null
>>>>> +++ b/drivers/hwmon/generic-pwm-tachometer.c
>>>>> @@ -0,0 +1,112 @@
>>>>> +/*
>>>>> + * Copyright (c) 2017-2018, NVIDIA CORPORATION. All rights reserved.
>>>>> + *
>>>>> + * This program is free software; you can redistribute it and/or
>>>>> modify it
>>>>> + * under the terms and conditions of the GNU General Public License,
>>>>> + * version 2, as published by the Free Software Foundation.
>>>>> + *
>>>>> + * This program is distributed in the hope it will be useful, but
>>>>> WITHOUT
>>>>> + * ANY WARRANTY; without even the implied warranty of
>>>>> MERCHANTABILITY or
>>>>> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
>>>>> License for
>>>>> + * more details.
>>>>> + *
>>>>> + */
>>>>> +
>>>>> +#include <linux/module.h>
>>>>> +#include <linux/platform_device.h>
>>>>> +#include <linux/err.h>
>>>>> +#include <linux/pwm.h>
>>>>> +#include <linux/hwmon.h>
>>>>> +#include <linux/hwmon-sysfs.h>
>>>>> +
>>>>> +struct pwm_hwmon_tach {
>>>>> + struct device *dev;
>>>>> + struct pwm_device *pwm;
>>>>> + struct device *hwmon;
>>>>> +};
>>>>> +
>>>>> +static ssize_t show_rpm(struct device *dev, struct
>>>>> device_attribute *attr,
>>>>> + char *buf)
>>>>> +{
>>>>> + struct pwm_hwmon_tach *ptt = dev_get_drvdata(dev);
>>>>> + struct pwm_device *pwm = ptt->pwm;
>>>>> + struct pwm_capture result;
>>>>> + int err;
>>>>> + unsigned int rpm = 0;
>>>>> +
>>>>> + err = pwm_capture(pwm, &result, 0);
>>>>> + if (err < 0) {
>>>>> + dev_err(ptt->dev, "Failed to capture PWM: %d\n", err);
>>>>> + return err;
>>>>> + }
>>>>> +
>>>>> + if (result.period)
>>>>> + rpm = DIV_ROUND_CLOSEST_ULL(60ULL * NSEC_PER_SEC,
>>>>> + result.period);
>>>>> +
>>>>> + return sprintf(buf, "%u\n", rpm);
>>>>> +}
>>>>> +
>>>>> +static SENSOR_DEVICE_ATTR(rpm, 0444, show_rpm, NULL, 0);
>>>>> +
>>>>> +static struct attribute *pwm_tach_attrs[] = {
>>>>> + &sensor_dev_attr_rpm.dev_attr.attr,
>>>>> + NULL,
>>>>> +};
>>>>
>>>> "rpm" is not a standard hwmon sysfs attribute. If you don't provide
>>>> a single standard hwmon sysfs attribute, having a hwmon driver is
>>>> pointless.
>>> Guenter Roeck,
>>> I will define a new hwmon sysfs attribute node called
>>> "hwmon_tachometer_attributes" in hwmon.h like below and update the
>>> same in tachometer hwmon driver. Is it fine ?
>>> enum hwmon_tachometer_attributes {
>>
>> Are you kidding me ?
>>
>> Guenter
> Sorry, I just wanted to confirm whether my understanding is correct or
> not before implementing it actually.
> Or, shall I add this attribute as a part of fan attributes with
> "hwmon_fan_rpm" ? or any other way to do it ? I need your inputs in
> fixing this.
I think he wants the attribute to be named according to the properties
in this document:
https://www.kernel.org/doc/Documentation/hwmon/sysfs-interface. I guess
the attribute would then map to fan1_input, though I'm not sure if
that's 100% correct either since this could technically be attached to
something other than a fan. But I would think in practice that's not a
big concern.
Guenter,
Please correct me as well if I'm wrong.
Thank you,
Mikko
>
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