On 02/28/2018 08:12 AM, Rajkumar Rampelli wrote:

On Wednesday 28 February 2018 11:28 AM, Guenter Roeck wrote:

quoted

On 02/27/2018 09:38 PM, Rajkumar Rampelli wrote:

quoted

On Wednesday 21 February 2018 08:20 PM, Guenter Roeck wrote:

quoted

On 02/20/2018 10:58 PM, Rajkumar Rampelli wrote:

quoted

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 <redacted>
---
? 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 [off-list ref]
+
+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 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.

Thank you,
Mikko

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