On Wednesday 21 February 2018 09:38 PM, Guenter Roeck wrote:
On Wed, Feb 21, 2018 at 05:20:29PM +0200, Mikko Perttunen wrote:
On 21.02.2018 16:46, Guenter Roeck wrote:
On 02/20/2018 11:15 PM, Mikko Perttunen wrote:
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.

I am kind of lost. Please explain.

Are you saying that we should drop the pwm-fan driver as well (which goes
the opposite way), as well as any other drivers doing anything with pwm
because after all those signals are already exposed to userspace a sysfs
and a kernel driver to abstract those values is thus not needed ?
The only thing this driver does is do a constant division in kernelspace.
I'm not really seeing why that couldn't be done in userspace. But if you
think it's appropriate to do the RPM conversion in kernelspace then I'm not
greatly opposed to that.

Isn't that true for any conversion from and to pwm values ? Voltages,
for example ? Should those be handled in userspace as well ?

Note that I am not entirely convinced that the approach suggested in this
patch series makes sense. Patch 4 seems to move the notion of a tachometer
into the pwm subsystem. I am not really convinced that this makes sense
(maybe all that code should be in the hwmon driver instead, or in a thermal
driver if the author prefers). But that is a different issue. The question
you raised is if there should be any abstraction to or from raw pwm values
in the kernel.
Since tachometer driver implements PWM capture callback feature, I have added it under pwm driver as pwm-tegra-tachometer.c driver. If the best approach is to have this tachometer driver under hwmon driver then I will move it to hwmon driver.

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

So you are saying there is no means to express in devicetree that
a pwm input is connected to a fan ? How is that not hardware ?

If so, how do you express in devicetree that a pwm signal is connected
to anything ?
If we want to describe that the tachometer is connected to a fan, then we
should have a fan node in the board's device tree. We don't have a chip that
has a thing called "generic-pwm-tachometer" attached to it. (We have chips
that have a "nvidia,tegra186-tachometer", so it's proper to have that.)

So you are concerned about the property name ? I don't really care how
it is called.





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 <rr...@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
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
+Tachometer controller that moniors the Fan speed in periods.
+Author: Rajkumar Rampelli <rr...@nvidia.com>
+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.

+    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.

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


diff --git a/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
+ * ANY WARRANTY; without even the implied warranty of
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
+            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)
+                        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,
+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_DESCRIPTION("PWM based Generic Tachometer driver");
+MODULE_AUTHOR("Laxman Dewangan <ldewan...@nvidia.com>");
+MODULE_AUTHOR("Rajkumar Rampelli <rr...@nvidia.com>");

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