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Subject: Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM
 based tachometer
To:     Rajkumar Rampelli <rrajk@nvidia.com>,
        Guenter Roeck <linux@roeck-us.net>, robh+dt@kernel.org,
        mark.rutland@arm.com, thierry.reding@gmail.com,
        jonathanh@nvidia.com, jdelvare@suse.com, corbet@lwn.net,
        catalin.marinas@arm.com, will.deacon@arm.com,
        kstewart@linuxfoundation.org, gregkh@linuxfoundation.org,
        pombredanne@nexb.com, mmaddireddy@nvidia.com,
        mperttunen@nvidia.com, arnd@arndb.de, timur@codeaurora.org,
        andy.gross@linaro.org, xuwei5@hisilicon.com, elder@linaro.org,
        heiko@sntech.de, krzk@kernel.org, ard.biesheuvel@linaro.org
Cc:     devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-pwm@vger.kernel.org, linux-tegra@vger.kernel.org,
        linux-hwmon@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, ldewangan@nvidia.com
References: <1519196339-9377-1-git-send-email-rrajk@nvidia.com>
 <1519196339-9377-6-git-send-email-rrajk@nvidia.com>
 <5172edff-fe29-7ed1-f0d2-b0359ea2c24d@roeck-us.net>
 <2510b525-ec36-b49d-5a62-81f335c0d10d@nvidia.com>
 <cfe0d0ce-3a89-bad0-85ba-6edf1135d2dc@roeck-us.net>
 <2628eff2-dd33-34f4-a7e1-cfe46ef88a3f@nvidia.com>
From:   Mikko Perttunen <cyndis@kapsi.fi>
Message-ID: <4556a8d2-947d-72c4-2962-3167afb53978@kapsi.fi>
Date:   Wed, 28 Feb 2018 09:03:48 +0200
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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@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.

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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