From ca8fd8c16a8b77dfcf7f6ce52d2c863220693a78 Mon Sep 17 00:00:00 2001

From: Armin Wolf <W_Armin@gmx.de>

Date: Sat, 24 Dec 2022 05:18:53 +0100

Subject: [PATCH] hwmon: (ftsteutates) Fix scaling of measurements

Git-commit: ca8fd8c16a8b77dfcf7f6ce52d2c863220693a78

Patch-mainline: v6.3-rc1

References: git-fixes

A user complained that the ftsteutates driver was displaying

bogus values since its introduction. This happens because the

sensor measurements need to be scaled in order to produce

meaningful results:

- the fan speed needs to be multiplied by 60 since its in RPS

- the temperature is in degrees celsius and needs an offset of 64

- the voltage is in 1/256 of 3.3V

The offical datasheet says the voltage needs to be divided by 256,

but this is likely an off-by-one-error, since even the BIOS

devides by 255 (otherwise 3.3V could not be measured).

The voltage channels additionally need a board-specific multiplier,

however this can be done by the driver since its board-specific.

The reason the missing scaling of measurements is the way Fujitsu

used this driver when it was still out-of-tree. Back then, all

scaling was done in userspace by libsensors, even the generic one.

Tested on a Fujitsu DS3401-B1.

Fixes: 08426eda58e0 ("hwmon: Add driver for FTS BMC chip "Teutates"")

Signed-off-by: Armin Wolf <W_Armin@gmx.de>

Link: https://lore.kernel.org/r/20221224041855.83981-2-W_Armin@gmx.de

Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 Documentation/hwmon/ftsteutates.rst |  4 ++++

 drivers/hwmon/ftsteutates.c         | 19 +++++++++++++------

 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/Documentation/hwmon/ftsteutates.rst b/Documentation/hwmon/ftsteutates.rst

index 58a2483d8d0d..198fa8e2819d 100644

--- a/Documentation/hwmon/ftsteutates.rst

+++ b/Documentation/hwmon/ftsteutates.rst

@@ -22,6 +22,10 @@ enhancements. It can monitor up to 4 voltages, 16 temperatures and

 8 fans. It also contains an integrated watchdog which is currently

 implemented in this driver.

+The 4 voltages require a board-specific multiplier, since the BMC can

+only measure voltages up to 3.3V and thus relies on voltage dividers.

+Consult your motherboard manual for details.

+

 To clear a temperature or fan alarm, execute the following command with the

 correct path to the alarm file::

diff --git a/drivers/hwmon/ftsteutates.c b/drivers/hwmon/ftsteutates.c

index f5b8e724a8ca..ffa0bb364877 100644

--- a/drivers/hwmon/ftsteutates.c

+++ b/drivers/hwmon/ftsteutates.c

@@ -12,6 +12,7 @@

 #include <linux/i2c.h>

 #include <linux/init.h>

 #include <linux/jiffies.h>

+#include <linux/math.h>

 #include <linux/module.h>

 #include <linux/mutex.h>

 #include <linux/slab.h>

@@ -347,13 +348,15 @@ static ssize_t in_value_show(struct device *dev,

 {

 	struct fts_data *data = dev_get_drvdata(dev);

 	int index = to_sensor_dev_attr(devattr)->index;

-	int err;

+	int value, err;

 	err = fts_update_device(data);

 	if (err < 0)

 		return err;

-	return sprintf(buf, "%u\n", data->volt[index]);

+	value = DIV_ROUND_CLOSEST(data->volt[index] * 3300, 255);

+

+	return sprintf(buf, "%d\n", value);

 }

 static ssize_t temp_value_show(struct device *dev,

@@ -361,13 +364,15 @@ static ssize_t temp_value_show(struct device *dev,

 {

 	struct fts_data *data = dev_get_drvdata(dev);

 	int index = to_sensor_dev_attr(devattr)->index;

-	int err;

+	int value, err;

 	err = fts_update_device(data);

 	if (err < 0)

 		return err;

-	return sprintf(buf, "%u\n", data->temp_input[index]);

+	value = (data->temp_input[index] - 64) * 1000;

+

+	return sprintf(buf, "%d\n", value);

 }

 static ssize_t temp_fault_show(struct device *dev,

@@ -436,13 +441,15 @@ static ssize_t fan_value_show(struct device *dev,

 {

 	struct fts_data *data = dev_get_drvdata(dev);

 	int index = to_sensor_dev_attr(devattr)->index;

-	int err;

+	int value, err;

 	err = fts_update_device(data);

 	if (err < 0)

 		return err;

-	return sprintf(buf, "%u\n", data->fan_input[index]);

+	value = data->fan_input[index] * 60;

+

+	return sprintf(buf, "%d\n", value);

 }

 static ssize_t fan_source_show(struct device *dev,

-- 

2.35.3