hwmon: Create an NSA320 hardware monitoring driver

Create a driver to support the hardware monitoring chip present in
the Zyxel NSA320 and some of the other Zyxel NAS devices.

The driver reads fan speed and temperature from a suitably
pre-programmed MCU on the device.

Signed-off-by: Adam Baker <[e-mail]>
[groeck: Dropped .owner field initialization]
Signed-off-by: Guenter Roeck <[e-mail]>

Documentation/hwmon/nsa320

···
+Kernel driver nsa320_hwmon
+==========================
+
+Supported chips:
+  * Holtek HT46R065 microcontroller with onboard firmware that configures
+	it to act as a hardware monitor.
+    Prefix: 'nsa320'
+    Addresses scanned: none
+    Datasheet: Not available, driver was reverse engineered based upon the
+	Zyxel kernel source
+
+Author:
+  Adam Baker <[e-mail]>
+
+Description
+-----------
+
+This chip is known to be used in the Zyxel NSA320 and NSA325 NAS Units and
+also in some variants of the NSA310 but the driver has only been tested
+on the NSA320. In all of these devices it is connected to the same 3 GPIO
+lines which are used to provide chip select, clock and data lines. The
+interface behaves similarly to SPI but at much lower speeds than are normally
+used for SPI.
+
+Following each chip select pulse the chip will generate a single 32 bit word
+that contains 0x55 as a marker to indicate that data is being read correctly,
+followed by an 8 bit fan speed in 100s of RPM and a 16 bit temperature in
+tenths of a degree.
+
+
+sysfs-Interface
+---------------
+
+temp1_input - temperature input
+fan1_input - fan speed
+
+Notes
+-----
+
+The access timings used in the driver are the same as used in the Zyxel
+provided kernel. Testing has shown that if the delay between chip select and
+the first clock pulse is reduced from 100 ms to just under 10ms then the chip
+will not produce any output. If the duration of either phase of the clock
+is reduced from 100 us to less than 15 us then data pulses are likely to be
+read twice corrupting the output. The above analysis is based upon a sample
+of one unit but suggests that the Zyxel provided delay values include a
+reasonable tolerance.
+
+The driver incorporates a limit that it will not check for updated values
+faster than once a second. This is because the hardware takes a relatively long
+time to read the data from the device and when it does it reads both temp and
+fan speed. As the most likely case for two accesses in quick succession is
+to read both of these values avoiding a second read delay is desirable.

drivers/hwmon/Kconfig

···
 	  This driver can also be built as a module.  If so, the module
 	  will be called nct7904.
 
+config SENSORS_NSA320
+	tristate "ZyXEL NSA320 and compatible fan speed and temperature sensors"
+	depends on GPIOLIB && OF
+	depends on MACH_KIRKWOOD || COMPILE_TEST
+	help
+	  If you say yes here you get support for hardware monitoring
+	  for the ZyXEL NSA320 Media Server and other compatible devices
+	  (probably the NSA325 and some NSA310 variants).
+
+	  The sensor data is taken from a Holtek HT46R065 microcontroller
+	  connected to GPIO lines.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called nsa320-hwmon.
+
 config SENSORS_PCF8591
 	tristate "Philips PCF8591 ADC/DAC"
 	depends on I2C

drivers/hwmon/Makefile

···
 obj-$(CONFIG_SENSORS_NCT6775)	+= nct6775.o
 obj-$(CONFIG_SENSORS_NCT7802)	+= nct7802.o
 obj-$(CONFIG_SENSORS_NCT7904)	+= nct7904.o
+obj-$(CONFIG_SENSORS_NSA320)	+= nsa320-hwmon.o
 obj-$(CONFIG_SENSORS_NTC_THERMISTOR)	+= ntc_thermistor.o
 obj-$(CONFIG_SENSORS_PC87360)	+= pc87360.o
 obj-$(CONFIG_SENSORS_PC87427)	+= pc87427.o

drivers/hwmon/nsa320-hwmon.c

···
+/*
+ * drivers/hwmon/nsa320-hwmon.c
+ *
+ * ZyXEL NSA320 Media Servers
+ * hardware monitoring
+ *
+ * Copyright (C) 2016 Adam Baker <[e-mail]>
+ * based on a board file driver
+ * Copyright (C) 2012 Peter Schildmann <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License v2 as published by the
+ * Free Software Foundation.
+ *
+ * This program is distributed in the hope that 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/bitops.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+
+/* Tests for error return values rely upon this value being < 0x80 */
+#define MAGIC_NUMBER 0x55
+
+/*
+ * The Zyxel hwmon MCU is a Holtek HT46R065 that is factory programmed
+ * to perform temperature and fan speed monitoring. It is read by taking
+ * the active pin low. The 32 bit output word is then clocked onto the
+ * data line. The MSB of the data word is a magic nuber to indicate it
+ * has been read correctly, the next byte is the fan speed (in hundreds
+ * of RPM) and the last two bytes are the temperature (in tenths of a
+ * degree)
+ */
+
+struct nsa320_hwmon {
+	struct mutex		update_lock;	/* lock GPIO operations */
+	unsigned long		last_updated;	/* jiffies */
+	unsigned long		mcu_data;
+	struct gpio_desc	*act;
+	struct gpio_desc	*clk;
+	struct gpio_desc	*data;
+};
+
+enum nsa320_inputs {
+	NSA320_TEMP = 0,
+	NSA320_FAN = 1,
+};
+
+static const char * const nsa320_input_names[] = {
+	[NSA320_TEMP] = "System Temperature",
+	[NSA320_FAN] = "Chassis Fan",
+};
+
+/*
+ * Although this protocol looks similar to SPI the long delay
+ * between the active (aka chip select) signal and the shorter
+ * delay between clock pulses are needed for reliable operation.
+ * The delays provided are taken from the manufacturer kernel,
+ * testing suggest they probably incorporate a reasonable safety
+ * margin. (The single device tested became unreliable if the
+ * delay was reduced to 1/10th of this value.)
+ */
+static s32 nsa320_hwmon_update(struct device *dev)
+{
+	u32 mcu_data;
+	u32 mask;
+	struct nsa320_hwmon *hwmon = dev_get_drvdata(dev);
+
+	mutex_lock(&hwmon->update_lock);
+
+	mcu_data = hwmon->mcu_data;
+
+	if (time_after(jiffies, hwmon->last_updated + HZ) || mcu_data == 0) {
+		gpiod_set_value(hwmon->act, 1);
+		msleep(100);
+
+		mcu_data = 0;
+		for (mask = BIT(31); mask; mask >>= 1) {
+			gpiod_set_value(hwmon->clk, 0);
+			usleep_range(100, 200);
+			gpiod_set_value(hwmon->clk, 1);
+			usleep_range(100, 200);
+			if (gpiod_get_value(hwmon->data))
+				mcu_data |= mask;
+		}
+
+		gpiod_set_value(hwmon->act, 0);
+		dev_dbg(dev, "Read raw MCU data %08x\n", mcu_data);
+
+		if ((mcu_data >> 24) != MAGIC_NUMBER) {
+			dev_dbg(dev, "Read invalid MCU data %08x\n", mcu_data);
+			mcu_data = -EIO;
+		} else {
+			hwmon->mcu_data = mcu_data;
+			hwmon->last_updated = jiffies;
+		}
+	}
+
+	mutex_unlock(&hwmon->update_lock);
+
+	return mcu_data;
+}
+
+static ssize_t show_label(struct device *dev,
+			  struct device_attribute *attr, char *buf)
+{
+	int channel = to_sensor_dev_attr(attr)->index;
+
+	return sprintf(buf, "%s\n", nsa320_input_names[channel]);
+}
+
+static ssize_t show_temp(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	s32 mcu_data = nsa320_hwmon_update(dev);
+
+	if (mcu_data < 0)
+		return mcu_data;
+
+	return sprintf(buf, "%d\n", (mcu_data & 0xffff) * 100);
+}
+
+static ssize_t show_fan(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	s32 mcu_data = nsa320_hwmon_update(dev);
+
+	if (mcu_data < 0)
+		return mcu_data;
+
+	return sprintf(buf, "%d\n", ((mcu_data & 0xff0000) >> 16) * 100);
+}
+
+static SENSOR_DEVICE_ATTR(temp1_label, S_IRUGO, show_label, NULL, NSA320_TEMP);
+static DEVICE_ATTR(temp1_input, S_IRUGO, show_temp, NULL);
+static SENSOR_DEVICE_ATTR(fan1_label, S_IRUGO, show_label, NULL, NSA320_FAN);
+static DEVICE_ATTR(fan1_input, S_IRUGO, show_fan, NULL);
+
+static struct attribute *nsa320_attrs[] = {
+	&sensor_dev_attr_temp1_label.dev_attr.attr,
+	&dev_attr_temp1_input.attr,
+	&sensor_dev_attr_fan1_label.dev_attr.attr,
+	&dev_attr_fan1_input.attr,
+	NULL
+};
+
+ATTRIBUTE_GROUPS(nsa320);
+
+static const struct of_device_id of_nsa320_hwmon_match[] = {
+	{ .compatible = "zyxel,nsa320-mcu", },
+	{ },
+};
+
+static int nsa320_hwmon_probe(struct platform_device *pdev)
+{
+	struct nsa320_hwmon	*hwmon;
+	struct device		*classdev;
+
+	hwmon = devm_kzalloc(&pdev->dev, sizeof(*hwmon), GFP_KERNEL);
+	if (!hwmon)
+		return -ENOMEM;
+
+	/* Look up the GPIO pins to use */
+	hwmon->act = devm_gpiod_get(&pdev->dev, "act", GPIOD_OUT_LOW);
+	if (IS_ERR(hwmon->act))
+		return PTR_ERR(hwmon->act);
+
+	hwmon->clk = devm_gpiod_get(&pdev->dev, "clk", GPIOD_OUT_HIGH);
+	if (IS_ERR(hwmon->clk))
+		return PTR_ERR(hwmon->clk);
+
+	hwmon->data = devm_gpiod_get(&pdev->dev, "data", GPIOD_IN);
+	if (IS_ERR(hwmon->data))
+		return PTR_ERR(hwmon->data);
+
+	mutex_init(&hwmon->update_lock);
+
+	classdev = devm_hwmon_device_register_with_groups(&pdev->dev,
+					"nsa320", hwmon, nsa320_groups);
+
+	return PTR_ERR_OR_ZERO(classdev);
+
+}
+
+/* All allocations use devres so remove() is not needed. */
+
+static struct platform_driver nsa320_hwmon_driver = {
+	.probe = nsa320_hwmon_probe,
+	.driver = {
+		.name = "nsa320-hwmon",
+		.of_match_table = of_match_ptr(of_nsa320_hwmon_match),
+	},
+};
+
+module_platform_driver(nsa320_hwmon_driver);
+
+MODULE_DEVICE_TABLE(of, of_nsa320_hwmon_match);
+MODULE_AUTHOR("Peter Schildmann <[e-mail]>");
+MODULE_AUTHOR("Adam Baker <[e-mail]>");
+MODULE_DESCRIPTION("NSA320 Hardware Monitoring");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:nsa320-hwmon");