[PATCH 1/2] lm73: added '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
temp1_update_interval attribute.  Full details on use of this mechanism
are described in Documentation/hwmon/lm73.

Signed-off-by: Chris Verges <kg4ysn@xxxxxxxxx>
---
 Documentation/hwmon/lm73 |   78 ++++++++++++++++++++++++++++++++++++++++++++++
 drivers/hwmon/lm73.c     |   76 +++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 150 insertions(+), 4 deletions(-)
 create mode 100644 Documentation/hwmon/lm73

diff --git a/Documentation/hwmon/lm73 b/Documentation/hwmon/lm73
new file mode 100644
index 0000000..2d947d3
--- /dev/null
+++ b/Documentation/hwmon/lm73
@@ -0,0 +1,78 @@
+Kernel driver lm90
+==================
+
+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: Chris Verges <kg4ysn@xxxxxxxxx>
+
+
+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..21
+    0.125         28            22..42
+    0.0625        56            43..84
+    0.03125       112           85..infinity
+    --------------------------------------
+
+The following examples show how the 'update_interval' attribute can be
+used to change the conversion time:
+
+    $ echo 0 > temp1_update_interval
+    $ cat temp1_update_interval
+    14
+    $ cat temp1_input
+    24250
+
+    $ echo 36 > temp1_update_interval
+    $ cat temp1_update_interval
+    28
+    $ cat temp1_input
+    24125
+
+    $ echo 56 > temp1_update_interval
+    $ cat temp1_update_interval
+    56
+    $ cat temp1_input
+    24062
+
+    $ echo 85 > temp1_update_interval
+    $ cat temp1_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.
diff --git a/drivers/hwmon/lm73.c b/drivers/hwmon/lm73.c
index 7272176..f443fad 100644
--- a/drivers/hwmon/lm73.c
+++ b/drivers/hwmon/lm73.c
@@ -21,7 +21,6 @@
 #include <linux/hwmon-sysfs.h>
 #include <linux/err.h>
 
-
 /* Addresses scanned */
 static const unsigned short normal_i2c[] = { 0x48, 0x49, 0x4a, 0x4c,
 					0x4d, 0x4e, I2C_CLIENT_END };
@@ -39,8 +38,20 @@ static const unsigned short normal_i2c[] = { 0x48, 0x49, 0x4a, 0x4c,
 #define LM73_TEMP_MIN		(-40)
 #define LM73_TEMP_MAX		150
 
-/*-----------------------------------------------------------------------*/
+#define LM73_CTRL_RES_SHIFT	5
+#define LM73_CTRL_RES_SIZE	2
+#define LM73_CTRL_RES_MASK	((1 << LM73_CTRL_RES_SIZE) - 1)
 
+#define SCALE_150_PERCENT(x)	(((x) * 150) / 100)
+
+static const unsigned short lm73_valid_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 */
+};
+
+/*-----------------------------------------------------------------------*/
 
 static ssize_t set_temp(struct device *dev, struct device_attribute *da,
 			const char *buf, size_t count)
@@ -79,6 +90,62 @@ 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);
+	unsigned long convrate;
+	s32 err;
+	u8 res_bits = 0;
+	u8 value;
+
+	err = kstrtoul(buf, 10, &convrate);
+	if (err < 0)
+		return err;
+
+	/* Read existing control value */
+	err = i2c_smbus_read_byte_data(client, LM73_REG_CTRL);
+	if (err < 0)
+		return err;
+	value = err;
+
+	/* Convert the desired conversion rate into register bits */
+	if (convrate < SCALE_150_PERCENT(lm73_valid_convrates[0]))
+		res_bits = 0;
+	else if (convrate < SCALE_150_PERCENT(lm73_valid_convrates[1]))
+		res_bits = 1;
+	else if (convrate < SCALE_150_PERCENT(lm73_valid_convrates[2]))
+		res_bits = 2;
+	else
+		res_bits = 3;
+
+	/* Create the new control register value */
+	value &= ~(LM73_CTRL_RES_MASK << LM73_CTRL_RES_SHIFT);
+	value |= (res_bits << LM73_CTRL_RES_SHIFT);
+
+	/* Write value */
+	err = i2c_smbus_write_byte_data(client, LM73_REG_CTRL, value);
+	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);
+	uint32_t ctrl;
+	u8 res_bits = 0;
+
+	/* Read existing control value */
+	ctrl = i2c_smbus_read_byte_data(client, LM73_REG_CTRL);
+	if (ctrl < 0)
+		return ctrl;
+
+	res_bits = (ctrl >> LM73_CTRL_RES_SHIFT) & LM73_CTRL_RES_MASK;
+	return scnprintf(buf, PAGE_SIZE, "%hu\n",
+			lm73_valid_convrates[res_bits]);
+}
 
 /*-----------------------------------------------------------------------*/
 
@@ -90,13 +157,14 @@ 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(temp1_update_interval, S_IWUSR | S_IRUGO,
+			show_convrate, set_convrate, LM73_REG_CTRL);
 
 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_temp1_update_interval.dev_attr.attr,
 	NULL
 };
 
-- 
1.7.9.5


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