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Subject: Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM
 based tachometer
To:     Rajkumar Rampelli <rrajk@nvidia.com>, 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>
From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <cfe0d0ce-3a89-bad0-85ba-6edf1135d2dc@roeck-us.net>
Date:   Tue, 27 Feb 2018 21:58:16 -0800
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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