hwmon: (ltc4245) Expose all GPIO pins as analog voltages

Add support for exposing all GPIO pins as analog voltages. Though this is
not an ideal use of the chip, some hardware engineers may decide that the
LTC4245 meets their design requirements when studying the datasheet.

The GPIO pins are sampled in round-robin fashion, meaning that a slow
reader will see stale data. A userspace application can detect this,
because it will get -EAGAIN when reading from a sysfs file which contains
stale data.

Users can choose to use this feature on a per-chip basis by using either
platform data or the OF device tree (where applicable).

Signed-off-by: Ira W. Snyder <[e-mail]>
Signed-off-by: Jean Delvare <[e-mail]>

Documentation/hwmon/ltc4245

···
 in7_min_alarm		3v  output undervoltage alarm
 in8_min_alarm		Vee (-12v) output undervoltage alarm
 
-in9_input		GPIO voltage data
+in9_input		GPIO voltage data (see note 1)
+in10_input		GPIO voltage data (see note 1)
+in11_input		GPIO voltage data (see note 1)
 
 power1_input		12v power usage (mW)
 power2_input		5v  power usage (mW)
 power3_input		3v  power usage (mW)
 power4_input		Vee (-12v) power usage (mW)
+
+
+Note 1
+------
+
+If you have NOT configured the driver to sample all GPIO pins as analog
+voltages, then the in10_input and in11_input sysfs attributes will not be
+created. The driver will sample the GPIO pin that is currently connected to the
+ADC as an analog voltage, and report the value in in9_input.
+
+If you have configured the driver to sample all GPIO pins as analog voltages,
+then they will be sampled in round-robin fashion. If userspace reads too
+slowly, -EAGAIN will be returned when you read the sysfs attribute containing
+the sensor reading.
+
+The LTC4245 chip can be configured to sample all GPIO pins with two methods:
+1) platform data -- see include/linux/i2c/ltc4245.h
+2) OF device tree -- add the "ltc4245,use-extra-gpios" property to each chip
+
+The default mode of operation is to sample a single GPIO pin.

drivers/hwmon/ltc4245.c

···
 #include <linux/i2c.h>
 #include <linux/hwmon.h>
 #include <linux/hwmon-sysfs.h>
+#include <linux/i2c/ltc4245.h>
 
 /* Here are names of the chip's registers (a.k.a. commands) */
 enum ltc4245_cmd {
···
 
 	/* Voltage registers */
 	u8 vregs[0x0d];
+
+	/* GPIO ADC registers */
+	bool use_extra_gpios;
+	int gpios[3];
 };
+
+/*
+ * Update the readings from the GPIO pins. If the driver has been configured to
+ * sample all GPIO's as analog voltages, a round-robin sampling method is used.
+ * Otherwise, only the configured GPIO pin is sampled.
+ *
+ * LOCKING: must hold data->update_lock
+ */
+static void ltc4245_update_gpios(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct ltc4245_data *data = i2c_get_clientdata(client);
+	u8 gpio_curr, gpio_next, gpio_reg;
+	int i;
+
+	/* no extra gpio support, we're basically done */
+	if (!data->use_extra_gpios) {
+		data->gpios[0] = data->vregs[LTC4245_GPIOADC - 0x10];
+		return;
+	}
+
+	/*
+	 * If the last reading was too long ago, then we mark all old GPIO
+	 * readings as stale by setting them to -EAGAIN
+	 */
+	if (time_after(jiffies, data->last_updated + 5 * HZ)) {
+		dev_dbg(&client->dev, "Marking GPIOs invalid\n");
+		for (i = 0; i < ARRAY_SIZE(data->gpios); i++)
+			data->gpios[i] = -EAGAIN;
+	}
+
+	/*
+	 * Get the current GPIO pin
+	 *
+	 * The datasheet calls these GPIO[1-3], but we'll calculate the zero
+	 * based array index instead, and call them GPIO[0-2]. This is much
+	 * easier to think about.
+	 */
+	gpio_curr = (data->cregs[LTC4245_GPIO] & 0xc0) >> 6;
+	if (gpio_curr > 0)
+		gpio_curr -= 1;
+
+	/* Read the GPIO voltage from the GPIOADC register */
+	data->gpios[gpio_curr] = data->vregs[LTC4245_GPIOADC - 0x10];
+
+	/* Find the next GPIO pin to read */
+	gpio_next = (gpio_curr + 1) % ARRAY_SIZE(data->gpios);
+
+	/*
+	 * Calculate the correct setting for the GPIO register so it will
+	 * sample the next GPIO pin
+	 */
+	gpio_reg = (data->cregs[LTC4245_GPIO] & 0x3f) | ((gpio_next + 1) << 6);
+
+	/* Update the GPIO register */
+	i2c_smbus_write_byte_data(client, LTC4245_GPIO, gpio_reg);
+
+	/* Update saved data */
+	data->cregs[LTC4245_GPIO] = gpio_reg;
+}
 
 static struct ltc4245_data *ltc4245_update_device(struct device *dev)
 {
···
 			else
 				data->vregs[i] = val;
 		}
+
+		/* Update GPIO readings */
+		ltc4245_update_gpios(dev);
 
 		data->last_updated = jiffies;
 		data->valid = 1;
···
 	return snprintf(buf, PAGE_SIZE, "%u\n", (reg & mask) ? 1 : 0);
 }
 
+static ssize_t ltc4245_show_gpio(struct device *dev,
+				 struct device_attribute *da,
+				 char *buf)
+{
+	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
+	struct ltc4245_data *data = ltc4245_update_device(dev);
+	int val = data->gpios[attr->index];
+
+	/* handle stale GPIO's */
+	if (val < 0)
+		return val;
+
+	/* Convert to millivolts and print */
+	return snprintf(buf, PAGE_SIZE, "%u\n", val * 10);
+}
+
 /* These macros are used below in constructing device attribute objects
  * for use with sysfs_create_group() to make a sysfs device file
  * for each register.
···
 #define LTC4245_ALARM(name, mask, reg) \
 	static SENSOR_DEVICE_ATTR_2(name, S_IRUGO, \
 	ltc4245_show_alarm, NULL, (mask), reg)
+
+#define LTC4245_GPIO_VOLTAGE(name, gpio_num) \
+	static SENSOR_DEVICE_ATTR(name, S_IRUGO, \
+	ltc4245_show_gpio, NULL, gpio_num)
 
 /* Construct a sensor_device_attribute structure for each register */
 
···
 LTC4245_ALARM(in8_min_alarm,	(1 << 3),	LTC4245_FAULT2);
 
 /* GPIO voltages */
-LTC4245_VOLTAGE(in9_input,			LTC4245_GPIOADC);
+LTC4245_GPIO_VOLTAGE(in9_input,			0);
+LTC4245_GPIO_VOLTAGE(in10_input,		1);
+LTC4245_GPIO_VOLTAGE(in11_input,		2);
 
 /* Power Consumption (virtual) */
 LTC4245_POWER(power1_input,			LTC4245_12VSENSE);
···
 /* Finally, construct an array of pointers to members of the above objects,
  * as required for sysfs_create_group()
  */
-static struct attribute *ltc4245_attributes[] = {
+static struct attribute *ltc4245_std_attributes[] = {
 	&sensor_dev_attr_in1_input.dev_attr.attr,
 	&sensor_dev_attr_in2_input.dev_attr.attr,
 	&sensor_dev_attr_in3_input.dev_attr.attr,
···
 	NULL,
 };
 
-static const struct attribute_group ltc4245_group = {
-	.attrs = ltc4245_attributes,
+static struct attribute *ltc4245_gpio_attributes[] = {
+	&sensor_dev_attr_in10_input.dev_attr.attr,
+	&sensor_dev_attr_in11_input.dev_attr.attr,
+	NULL,
 };
+
+static const struct attribute_group ltc4245_std_group = {
+	.attrs = ltc4245_std_attributes,
+};
+
+static const struct attribute_group ltc4245_gpio_group = {
+	.attrs = ltc4245_gpio_attributes,
+};
+
+static int ltc4245_sysfs_create_groups(struct i2c_client *client)
+{
+	struct ltc4245_data *data = i2c_get_clientdata(client);
+	struct device *dev = &client->dev;
+	int ret;
+
+	/* register the standard sysfs attributes */
+	ret = sysfs_create_group(&dev->kobj, &ltc4245_std_group);
+	if (ret) {
+		dev_err(dev, "unable to register standard attributes\n");
+		return ret;
+	}
+
+	/* if we're using the extra gpio support, register it's attributes */
+	if (data->use_extra_gpios) {
+		ret = sysfs_create_group(&dev->kobj, &ltc4245_gpio_group);
+		if (ret) {
+			dev_err(dev, "unable to register gpio attributes\n");
+			sysfs_remove_group(&dev->kobj, &ltc4245_std_group);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static void ltc4245_sysfs_remove_groups(struct i2c_client *client)
+{
+	struct ltc4245_data *data = i2c_get_clientdata(client);
+	struct device *dev = &client->dev;
+
+	if (data->use_extra_gpios)
+		sysfs_remove_group(&dev->kobj, &ltc4245_gpio_group);
+
+	sysfs_remove_group(&dev->kobj, &ltc4245_std_group);
+}
+
+static bool ltc4245_use_extra_gpios(struct i2c_client *client)
+{
+	struct ltc4245_platform_data *pdata = dev_get_platdata(&client->dev);
+#ifdef CONFIG_OF
+	struct device_node *np = client->dev.of_node;
+#endif
+
+	/* prefer platform data */
+	if (pdata)
+		return pdata->use_extra_gpios;
+
+#ifdef CONFIG_OF
+	/* fallback on OF */
+	if (of_find_property(np, "ltc4245,use-extra-gpios", NULL))
+		return true;
+#endif
+
+	return false;
+}
 
 static int ltc4245_probe(struct i2c_client *client,
 			 const struct i2c_device_id *id)
···
 
 	i2c_set_clientdata(client, data);
 	mutex_init(&data->update_lock);
+	data->use_extra_gpios = ltc4245_use_extra_gpios(client);
 
 	/* Initialize the LTC4245 chip */
 	i2c_smbus_write_byte_data(client, LTC4245_FAULT1, 0x00);
 	i2c_smbus_write_byte_data(client, LTC4245_FAULT2, 0x00);
 
 	/* Register sysfs hooks */
-	ret = sysfs_create_group(&client->dev.kobj, &ltc4245_group);
+	ret = ltc4245_sysfs_create_groups(client);
 	if (ret)
-		goto out_sysfs_create_group;
+		goto out_sysfs_create_groups;
 
 	data->hwmon_dev = hwmon_device_register(&client->dev);
 	if (IS_ERR(data->hwmon_dev)) {
···
 	return 0;
 
 out_hwmon_device_register:
-	sysfs_remove_group(&client->dev.kobj, &ltc4245_group);
-out_sysfs_create_group:
+	ltc4245_sysfs_remove_groups(client);
+out_sysfs_create_groups:
 	kfree(data);
 out_kzalloc:
 	return ret;
···
 	struct ltc4245_data *data = i2c_get_clientdata(client);
 
 	hwmon_device_unregister(data->hwmon_dev);
-	sysfs_remove_group(&client->dev.kobj, &ltc4245_group);
-
+	ltc4245_sysfs_remove_groups(client);
 	kfree(data);
 
 	return 0;

include/linux/i2c/ltc4245.h

···
+/*
+ * Platform Data for LTC4245 hardware monitor chip
+ *
+ * Copyright (c) 2010 Ira W. Snyder <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ */
+
+#ifndef LINUX_LTC4245_H
+#define LINUX_LTC4245_H
+
+#include <linux/types.h>
+
+struct ltc4245_platform_data {
+	bool use_extra_gpios;
+};
+
+#endif /* LINUX_LTC4245_H */