Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM
 based tachometer
To:     Guenter Roeck <linux@roeck-us.net>,
        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
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>
 <c1192f75-0e6e-c735-67e1-2901624831ae@roeck-us.net>
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
From:   Mikko Perttunen <cyndis@kapsi.fi>
Message-ID: <a5db25f7-6999-ff3a-21c2-161cfcf4db35@kapsi.fi>
Date:   Wed, 21 Feb 2018 17:20:29 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101
 Thunderbird/45.2.0
MIME-Version: 1.0
In-Reply-To: <c1192f75-0e6e-c735-67e1-2901624831ae@roeck-us.net>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 21.02.2018 16:46, Guenter Roeck wrote:
> 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 ?

The only thing this driver does is do a constant division in 
kernelspace. I'm not really seeing why that couldn't be done in 
userspace. But if you think it's appropriate to do the RPM conversion in 
kernelspace then I'm not greatly opposed to that.

>
>> 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 ?

If we want to describe that the tachometer is connected to a fan, then 
we should have a fan node in the board's device tree. We don't have a 
chip that has a thing called "generic-pwm-tachometer" attached to it. 
(We have chips that have a "nvidia,tegra186-tachometer", so it's proper 
to have that.)

Thanks,
Mikko

>
> 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");
>>>
>>
>