Message-ID: <73ca5840-865b-b44e-45e6-703b7749fb6f@nvidia.com>
Date:   Thu, 8 Mar 2018 09:57:22 +0200
From:   Mikko Perttunen <mperttunen@...dia.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Rajkumar Rampelli <rrajk@...dia.com>,
        Mikko Perttunen <cyndis@...si.fi>, <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>, <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 07.03.2018 16:20, Guenter Roeck wrote:
> On 03/07/2018 01:47 AM, Rajkumar Rampelli wrote:
>>
>>
>> On Wednesday 28 February 2018 07:59 PM, Guenter Roeck wrote:
>>> On 02/27/2018 11:03 PM, Mikko Perttunen wrote:
>>>> 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.
>>>>
>>> You are absolutely correct.
>>>
>>> While I am not opposed to ABI changes, the merits of those would need
>>> to be
>>> discussed on the mailing list. But replacing "fan1_input" with "rpm" is
>>> not an acceptable ABI change, even if it may measure something that
>>> turns
>>> but isn't a fan.
>>>
>>> If this _is_ in fact supposed to be used for something else but fans, we
>>> would have to discuss what that might be, and if hwmon is the
>>> appropriate
>>> subsystem to measure and report it. This does to some degree lead
>>> back to
>>> my concern of having the "fan" part of this patch series in the pwm
>>> core.
>>> I am still not sure if that makes sense.
>>>
>>> Thanks,
>>> Guenter
>> I am planning to add tachometer support in pwm-fan.c driver
>> (drivers/hwmon/) instead of adding new generic-pwm-tachometer.c
>> driver. Measuring RPM value will be done in pwm-fan driver itself
>> using pwm capture feature and will add new sysfs attributes under this
>> driver to report rpm value of fan.
>
> There is an existing attribute to report the RPM of fans. It is called
> fan[1..n]_input.
>
> "replacing "fan1_input" with "rpm" is not an acceptable ABI change"
>
> Preemptive NACK.
>
> Guenter
>

I think the idea here (based on personal discussion with Rajkumar) was 
to add a "new" sysfs attribute the driver exports, but that attribute 
would be the existing fan[1..n]_input.

Mikko

>>>
>>>> Thank you,
>>>> Mikko
>>>>
>>>>>
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>>>
>>
>>
>

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