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Subject: Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM
 based tachometer
To:     Mikko Perttunen <cyndis@kapsi.fi>,
        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,
        gregory.clement@free-electrons.com, 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>
 <ee03e1e5-bbeb-1238-04ed-b992fe3a3ce6@kapsi.fi>
From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <c1192f75-0e6e-c735-67e1-2901624831ae@roeck-us.net>
Date:   Wed, 21 Feb 2018 06:46:23 -0800
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On 02/20/2018 11:15 PM, Mikko Perttunen wrote:
> AIUI, the PWM framework already exposes a sysfs node with period information. We should just use that instead of adding a new driver for this.
> 

I am kind of lost. Please explain.

Are you saying that we should drop the pwm-fan driver as well (which goes
the opposite way), as well as any other drivers doing anything with pwm signals,
because after all those signals are already exposed to userspace a sysfs attributes,
and a kernel driver to abstract those values is thus not needed ?

> In any case, we cannot add something like this to device tree since it's not a hardware device.
> 

So you are saying there is no means to express in devicetree that
a pwm input is connected to a fan ? How is that not hardware ?

If so, how do you express in devicetree that a pwm signal is connected
to anything ?

Guenter

> Mikko
> 
> On 21.02.2018 08:58, 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,
>> +};
>> +
>> +ATTRIBUTE_GROUPS(pwm_tach);
>> +
>> +static int pwm_tach_probe(struct platform_device *pdev)
>> +{
>> +??? struct pwm_hwmon_tach *ptt;
>> +??? int err;
>> +
>> +??? ptt = devm_kzalloc(&pdev->dev, sizeof(*ptt), GFP_KERNEL);
>> +??? if (!ptt)
>> +??????? return -ENOMEM;
>> +
>> +??? ptt->dev = &pdev->dev;
>> +
>> +??? platform_set_drvdata(pdev, ptt);
>> +??? dev_set_drvdata(&pdev->dev, ptt);
>> +
>> +??? ptt->pwm = devm_of_pwm_get(&pdev->dev, pdev->dev.of_node, NULL);
>> +??? if (IS_ERR(ptt->pwm)) {
>> +??????? err = PTR_ERR(ptt->pwm);
>> +??????? dev_err(&pdev->dev, "Failed to get pwm handle, err: %d\n",
>> +??????????? err);
>> +??????? return err;
>> +??? }
>> +
>> +??? ptt->hwmon = devm_hwmon_device_register_with_groups(&pdev->dev,
>> +???????????????????? "pwm_tach", ptt, pwm_tach_groups);
>> +??? if (IS_ERR(ptt->hwmon)) {
>> +??????? err = PTR_ERR_OR_ZERO(ptt->hwmon);
>> +??????? dev_err(&pdev->dev, "Failed to register hwmon device: %d\n",
>> +??????????? err);
>> +??????? return err;
>> +??? }
>> +
>> +??? return 0;
>> +}
>> +
>> +static const struct of_device_id pwm_tach_of_match[] = {
>> +??? { .compatible = "generic-pwm-tachometer" },
>> +??? {}
>> +};
>> +MODULE_DEVICE_TABLE(of, pwm_tach_of_match);
>> +
>> +static struct platform_driver pwm_tach_driver = {
>> +??? .driver = {
>> +??????? .name = "generic-pwm-tachometer",
>> +??????? .of_match_table = pwm_tach_of_match,
>> +??? },
>> +??? .probe = pwm_tach_probe,
>> +};
>> +
>> +module_platform_driver(pwm_tach_driver);
>> +
>> +MODULE_DESCRIPTION("PWM based Generic Tachometer driver");
>> +MODULE_AUTHOR("Laxman Dewangan <ldewangan@nvidia.com>");
>> +MODULE_AUTHOR("Rajkumar Rampelli <rrajk@nvidia.com>");
>> +MODULE_LICENSE("GPL v2");
>>
>