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

From: Mikko Perttunen
Date: Wed Feb 21 2018 - 02:15:39 EST

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.

In any case, we cannot add something like this to device tree since it's not a hardware device.

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@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
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@xxxxxxxxxx>");
+MODULE_AUTHOR("Rajkumar Rampelli <rrajk@xxxxxxxxxx>");
+MODULE_LICENSE("GPL v2");