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Subject: Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM
 based tachometer
To:     Guenter Roeck <linux@roeck-us.net>, <robh+dt@kernel.org>,
        <mark.rutland@arm.com>, <thierry.reding@gmail.com>,
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From:   Rajkumar Rampelli <rrajk@nvidia.com>
Message-ID: <2628eff2-dd33-34f4-a7e1-cfe46ef88a3f@nvidia.com>
Date:   Wed, 28 Feb 2018 11:42:28 +0530
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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@nvidia.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@nvidia.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.