From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guenter Roeck Subject: Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM based tachometer Date: Thu, 8 Mar 2018 06:33:03 -0800 Message-ID: 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> <2628eff2-dd33-34f4-a7e1-cfe46ef88a3f@nvidia.com> <4556a8d2-947d-72c4-2962-3167afb53978@kapsi.fi> <62ba7f67-5a99-51ab-1214-eb68ebb7e642@roeck-us.net> <952cb50e-d9a0-ae5e-d9f6-d1ce268f0384@nvidia.com> <73ca5840-865b-b44e-45e6-703b7749fb6f@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <73ca5840-865b-b44e-45e6-703b7749fb6f@nvidia.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Mikko Perttunen , Rajkumar Rampelli , Mikko Perttunen , 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, 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 List-Id: linux-tegra@vger.kernel.org On 03/07/2018 11:57 PM, Mikko Perttunen wrote: > > > 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 >>>>>>>>>> --- >>>>>>>>>>   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 >>>>>>>>>> + >>>>>>>>>> +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 >>>>>>>>>> +#include >>>>>>>>>> +#include >>>>>>>>>> +#include >>>>>>>>>> +#include >>>>>>>>>> +#include >>>>>>>>>> + >>>>>>>>>> +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. > Ah, sorry, in this case misunderstanding on my side. Guenter