Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM based tachometer

From: Mikko Perttunen
Date: Wed Feb 28 2018 - 02:04:10 EST

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 <rrajk@xxxxxxxxxx>
---
 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@xxxxxxxxxx>
+
+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
ÂÂÂÂÂÂÂ If you say yes here you get support for the temperature
ÂÂÂÂÂÂÂ and power sensors for APM X-Gene SoC.
 +config GENERIC_PWM_TACHOMETER
+ÂÂÂ tristate "Generic PWM based tachometer driver"
+ÂÂÂ depends on PWM
+ÂÂÂ help
+ÂÂÂÂÂ Enables a driver to use PWM signal from motor to use
+ÂÂÂÂÂ for measuring the motor speed. The RPM is captured by
+ÂÂÂÂÂ PWM modules which has PWM capture capability and this
+ÂÂÂÂÂ drivers reads the captured data from PWM IP to convert
+ÂÂÂÂÂ it to speed in RPM.
+
 if ACPI
ÂÂÂ 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-$(CONFIG_SENSORS_WM8350)ÂÂÂ += wm8350-hwmon.o
 obj-$(CONFIG_SENSORS_XGENE) += xgene-hwmon.o
ÂÂÂ obj-$(CONFIG_PMBUS)ÂÂÂÂÂÂÂ += pmbus/
+obj-$(CONFIG_GENERIC_PWM_TACHOMETER) += generic-pwm-tachometer.o
ÂÂÂ 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 {
+ÂÂÂ struct deviceÂÂÂÂÂÂÂ *dev;
+ÂÂÂ struct pwm_deviceÂÂÂ *pwm;
+ÂÂÂ struct deviceÂÂÂÂÂÂÂ *hwmon;
+};
+
+static ssize_t show_rpm(struct device *dev, struct device_attribute *attr,
+ÂÂÂÂÂÂÂÂÂÂÂ char *buf)
+{
+ÂÂÂ struct pwm_hwmon_tach *ptt = dev_get_drvdata(dev);
+ÂÂÂ struct pwm_device *pwm = ptt->pwm;
+ÂÂÂ struct pwm_capture result;
+ÂÂÂ int err;
+ÂÂÂ unsigned int rpm = 0;
+
+ÂÂÂ err = pwm_capture(pwm, &result, 0);
+ÂÂÂ if (err < 0) {
+ÂÂÂÂÂÂÂ dev_err(ptt->dev, "Failed to capture PWM: %d\n", err);
+ÂÂÂÂÂÂÂ return err;
+ÂÂÂ }
+
+ÂÂÂ if (result.period)
+ÂÂÂÂÂÂÂ rpm = DIV_ROUND_CLOSEST_ULL(60ULL * NSEC_PER_SEC,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ result.period);
+
+ÂÂÂ return sprintf(buf, "%u\n", rpm);
+}
+
+static SENSOR_DEVICE_ATTR(rpm, 0444, show_rpm, NULL, 0);
+
+static struct attribute *pwm_tach_attrs[] = {
+ÂÂÂ &sensor_dev_attr_rpm.dev_attr.attr,
+ÂÂÂ 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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