lkml.org 
[lkml]   [2018]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM based tachometer
    From
    Date

    On Wednesday 21 February 2018 09:38 PM, Guenter Roeck wrote:
    > On Wed, Feb 21, 2018 at 05:20:29PM +0200, Mikko Perttunen wrote:
    >> 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.
    >>
    > Isn't that true for any conversion from and to pwm values ? Voltages,
    > for example ? Should those be handled in userspace as well ?
    >
    > Note that I am not entirely convinced that the approach suggested in this
    > patch series makes sense. Patch 4 seems to move the notion of a tachometer
    > into the pwm subsystem. I am not really convinced that this makes sense
    > (maybe all that code should be in the hwmon driver instead, or in a thermal
    > driver if the author prefers). But that is a different issue. The question
    > you raised is if there should be any abstraction to or from raw pwm values
    > in the kernel.
    Since tachometer driver implements PWM capture callback feature, I have
    added it under pwm driver as pwm-tegra-tachometer.c driver.
    If the best approach is to have this tachometer driver under hwmon
    driver then I will move it to hwmon driver.
    >
    >>>> 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.)
    >>
    > So you are concerned about the property name ? I don't really care how
    > it is called.
    >
    > Guenter
    >
    >> 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");
    >>>>>

    \
     
     \ /
      Last update: 2018-02-23 12:46    [W:4.139 / U:1.184 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site