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

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 <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