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hwmon: (lm73) Add 'update_interval' attribute

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The LM73 supports four A/D conversion resolutions.  The default used by
the existing lm73 driver is the chip's default, 11-bit (0.25 C/LSB).
This patch enables changing of this resolution from userspace via the
update_interval sysfs attribute.  Full details on usage are included in
Documentation/hwmon/lm73.

Signed-off-by: Chris Verges <kg4ysn@gmail.com>
[linux@roeck-us.net: cleanup]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Chris Verges 2013-01-05 01:41:19 -08:00 committed by Guenter Roeck
parent 91bba68801
commit 8c14d126ae
2 changed files with 165 additions and 11 deletions
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79
Documentation/hwmon/lm73 Normal file
View File

@ -0,0 +1,79 @@
Kernel driver lm73
==================
Supported chips:
* Texas Instruments LM73
Prefix: 'lm73'
Addresses scanned: I2C 0x48, 0x49, 0x4a, 0x4c, 0x4d, and 0x4e
Datasheet: Publicly available at the Texas Instruments website
http://www.ti.com/product/lm73
Author: Guillaume Ligneul <guillaume.ligneul@gmail.com>
Documentation: Chris Verges <kg4ysn@gmail.com>
Description
-----------
The LM73 is a digital temperature sensor. All temperature values are
given in degrees Celsius.
Measurement Resolution Support
------------------------------
The LM73 supports four resolutions, defined in terms of degrees C per
LSB: 0.25, 0.125, 0.0625, and 0.3125. Changing the resolution mode
affects the conversion time of the LM73's analog-to-digital converter.
From userspace, the desired resolution can be specified as a function of
conversion time via the 'update_interval' sysfs attribute for the
device. This attribute will normalize ranges of input values to the
maximum times defined for the resolution in the datasheet.
Resolution Conv. Time Input Range
(C/LSB) (msec) (msec)
--------------------------------------
0.25 14 0..14
0.125 28 15..28
0.0625 56 29..56
0.03125 112 57..infinity
--------------------------------------
The following examples show how the 'update_interval' attribute can be
used to change the conversion time:
$ echo 0 > update_interval
$ cat update_interval
14
$ cat temp1_input
24250
$ echo 22 > update_interval
$ cat update_interval
28
$ cat temp1_input
24125
$ echo 56 > update_interval
$ cat update_interval
56
$ cat temp1_input
24062
$ echo 85 > update_interval
$ cat update_interval
112
$ cat temp1_input
24031
As shown here, the lm73 driver automatically adjusts any user input for
'update_interval' via a step function. Reading back the
'update_interval' value after a write operation will confirm the
conversion time actively in use.
Mathematically, the resolution can be derived from the conversion time
via the following function:
g(x) = 0.250 * [log(x/14) / log(2)]
where 'x' is the output from 'update_interval' and 'g(x)' is the
resolution in degrees C per LSB.

97
drivers/hwmon/lm73.c
View File

@ -39,8 +39,24 @@ static const unsigned short normal_i2c[] = { 0x48, 0x49, 0x4a, 0x4c,
#define LM73_TEMP_MIN (-256000 / 250)
#define LM73_TEMP_MAX (255750 / 250)
/*-----------------------------------------------------------------------*/
#define LM73_CTRL_RES_SHIFT 5
#define LM73_CTRL_RES_MASK (BIT(5) | BIT(6))
#define LM73_CTRL_TO_MASK BIT(7)
static const unsigned short lm73_convrates[] = {
14, /* 11-bits (0.25000 C/LSB): RES1 Bit = 0, RES0 Bit = 0 */
28, /* 12-bits (0.12500 C/LSB): RES1 Bit = 0, RES0 Bit = 1 */
56, /* 13-bits (0.06250 C/LSB): RES1 Bit = 1, RES0 Bit = 0 */
112, /* 14-bits (0.03125 C/LSB): RES1 Bit = 1, RES0 Bit = 1 */
};
struct lm73_data {
struct device *hwmon_dev;
struct mutex lock;
u8 ctrl; /* control register value */
};
/*-----------------------------------------------------------------------*/
static ssize_t set_temp(struct device *dev, struct device_attribute *da,
const char *buf, size_t count)
@ -78,6 +94,51 @@ static ssize_t show_temp(struct device *dev, struct device_attribute *da,
return scnprintf(buf, PAGE_SIZE, "%d\n", temp);
}
static ssize_t set_convrate(struct device *dev, struct device_attribute *da,
const char *buf, size_t count)
{
struct i2c_client *client = to_i2c_client(dev);
struct lm73_data *data = i2c_get_clientdata(client);
unsigned long convrate;
s32 err;
int res = 0;
err = kstrtoul(buf, 10, &convrate);
if (err < 0)
return err;
/*
* Convert the desired conversion rate into register bits.
* res is already initialized, and everything past the second-to-last
* value in the array is treated as belonging to the last value
* in the array.
*/
while (res < (ARRAY_SIZE(lm73_convrates) - 1) &&
convrate > lm73_convrates[res])
res++;
mutex_lock(&data->lock);
data->ctrl &= LM73_CTRL_TO_MASK;
data->ctrl |= res << LM73_CTRL_RES_SHIFT;
err = i2c_smbus_write_byte_data(client, LM73_REG_CTRL, data->ctrl);
mutex_unlock(&data->lock);
if (err < 0)
return err;
return count;
}
static ssize_t show_convrate(struct device *dev, struct device_attribute *da,
char *buf)
{
struct i2c_client *client = to_i2c_client(dev);
struct lm73_data *data = i2c_get_clientdata(client);
int res;
res = (data->ctrl & LM73_CTRL_RES_MASK) >> LM73_CTRL_RES_SHIFT;
return scnprintf(buf, PAGE_SIZE, "%hu\n", lm73_convrates[res]);
}
/*-----------------------------------------------------------------------*/
@ -89,13 +150,14 @@ static SENSOR_DEVICE_ATTR(temp1_min, S_IWUSR | S_IRUGO,
show_temp, set_temp, LM73_REG_MIN);
static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
show_temp, NULL, LM73_REG_INPUT);
static SENSOR_DEVICE_ATTR(update_interval, S_IWUSR | S_IRUGO,
show_convrate, set_convrate, 0);
static struct attribute *lm73_attributes[] = {
&sensor_dev_attr_temp1_input.dev_attr.attr,
&sensor_dev_attr_temp1_max.dev_attr.attr,
&sensor_dev_attr_temp1_min.dev_attr.attr,
&sensor_dev_attr_update_interval.dev_attr.attr,
NULL
};
@ -110,23 +172,36 @@ static const struct attribute_group lm73_group = {
static int
lm73_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
struct device *hwmon_dev;
int status;
struct lm73_data *data;
int ctrl;
data = devm_kzalloc(&client->dev, sizeof(struct lm73_data),
GFP_KERNEL);
if (!data)
return -ENOMEM;
i2c_set_clientdata(client, data);
mutex_init(&data->lock);
ctrl = i2c_smbus_read_byte_data(client, LM73_REG_CTRL);
if (ctrl < 0)
return ctrl;
data->ctrl = ctrl;
/* Register sysfs hooks */
status = sysfs_create_group(&client->dev.kobj, &lm73_group);
if (status)
return status;
hwmon_dev = hwmon_device_register(&client->dev);
if (IS_ERR(hwmon_dev)) {
status = PTR_ERR(hwmon_dev);
data->hwmon_dev = hwmon_device_register(&client->dev);
if (IS_ERR(data->hwmon_dev)) {
status = PTR_ERR(data->hwmon_dev);
goto exit_remove;
}
i2c_set_clientdata(client, hwmon_dev);
dev_info(&client->dev, "%s: sensor '%s'\n",
dev_name(hwmon_dev), client->name);
dev_name(data->hwmon_dev), client->name);
return 0;
@ -137,9 +212,9 @@ exit_remove:
static int lm73_remove(struct i2c_client *client)
{
struct device *hwmon_dev = i2c_get_clientdata(client);
struct lm73_data *data = i2c_get_clientdata(client);
hwmon_device_unregister(hwmon_dev);
hwmon_device_unregister(data->hwmon_dev);
sysfs_remove_group(&client->dev.kobj, &lm73_group);
return 0;
}