From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-path: Subject: Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM based tachometer To: Guenter Roeck , , , , , , , , , , , , , , , , , , , , , 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> CC: , , , , , , , From: Rajkumar Rampelli Message-ID: <901cf469-1f7d-23f2-e42f-4ea133ef12fc@nvidia.com> Date: Wed, 28 Feb 2018 11:37:40 +0530 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/alternative; boundary="------------69219CEED6A8032BB783A7C8" List-ID: --------------69219CEED6A8032BB783A7C8 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit 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 that 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 anyother way to do it ? I need your inputs in fixing it. --------------69219CEED6A8032BB783A7C8 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: 8bit
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 <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
Sorry, I just wanted to confirm that 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 anyother way to do it ? I need your inputs in fixing it.
--------------69219CEED6A8032BB783A7C8-- From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM based tachometer 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: Rajkumar Rampelli Message-ID: <901cf469-1f7d-23f2-e42f-4ea133ef12fc@nvidia.com> Date: Wed, 28 Feb 2018 11:37:40 +0530 MIME-Version: 1.0 In-Reply-To: Return-Path: rrajk@nvidia.com Content-Type: multipart/alternative; boundary="------------69219CEED6A8032BB783A7C8" List-ID: To: Guenter Roeck , 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 --------------69219CEED6A8032BB783A7C8 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit 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 that 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 anyother way to do it ? I need your inputs in fixing it. --------------69219CEED6A8032BB783A7C8 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: 8bit
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 <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
Sorry, I just wanted to confirm that 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 anyother way to do it ? I need your inputs in fixing it.
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