W1: feature, w1_therm.c use strong pullup and documentation
authorDavid Fries <david@fries.net>
Thu, 16 Oct 2008 05:04:43 +0000 (22:04 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 16 Oct 2008 18:21:49 +0000 (11:21 -0700)
Added strong pullup to thermal sensor driver and general documentation on
the sensor.

Signed-off-by: David Fries <david@fries.net>
Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Documentation/w1/slaves/00-INDEX [new file with mode: 0644]
Documentation/w1/slaves/w1_therm [new file with mode: 0644]

index 5270cf4cb109f93a1505e4185f318a60f1fcd252..cb49802745dcb1c7838223b77d59c11e8e108b6b 100644 (file)
@@ -1,5 +1,7 @@
        - This file
+       - Drivers that provide support for specific family codes.
        - Individual chips providing 1-wire busses.
diff --git a/Documentation/w1/slaves/00-INDEX b/Documentation/w1/slaves/00-INDEX
new file mode 100644 (file)
index 0000000..f8101d6
--- /dev/null
@@ -0,0 +1,4 @@
+       - This file
+       - The Maxim/Dallas Semiconductor ds18*20 temperature sensor.
diff --git a/Documentation/w1/slaves/w1_therm b/Documentation/w1/slaves/w1_therm
new file mode 100644 (file)
index 0000000..0403aaa
--- /dev/null
@@ -0,0 +1,41 @@
+Kernel driver w1_therm
+Supported chips:
+  * Maxim ds18*20 based temperature sensors.
+Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
+w1_therm provides basic temperature conversion for ds18*20 devices.
+supported family codes:
+W1_THERM_DS18S20       0x10
+W1_THERM_DS1822                0x22
+W1_THERM_DS18B20       0x28
+Support is provided through the sysfs w1_slave file.  Each open and
+read sequence will initiate a temperature conversion then provide two
+lines of ASCII output.  The first line contains the nine hex bytes
+read along with a calculated crc value and YES or NO if it matched.
+If the crc matched the returned values are retained.  The second line
+displays the retained values along with a temperature in millidegrees
+Centigrade after t=.
+Parasite powered devices are limited to one slave performing a
+temperature conversion at a time.  If none of the devices are parasite
+powered it would be possible to convert all the devices at the same
+time and then go back to read individual sensors.  That isn't
+currently supported.  The driver also doesn't support reduced
+precision (which would also reduce the conversion time).
+The module parameter strong_pullup can be set to 0 to disable the
+strong pullup or 1 to enable.  If enabled the 5V strong pullup will be
+enabled when the conversion is taking place provided the master driver
+must support the strong pullup (or it falls back to a pullup
+resistor).  The DS18b20 temperature sensor specification lists a
+maximum current draw of 1.5mA and that a 5k pullup resistor is not
+sufficient.  The strong pullup is designed to provide the additional
+current required.
index fb28acaeed6c4ab01235f09b764b8d0b7e1b20b6..e87f464a6fb0adbd0c224e8951751f510bf5572a 100644 (file)
@@ -37,6 +37,14 @@ MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Evgeniy Polyakov <johnpol@2ka.mipt.ru>");
 MODULE_DESCRIPTION("Driver for 1-wire Dallas network protocol, temperature family.");
+/* Allow the strong pullup to be disabled, but default to enabled.
+ * If it was disabled a parasite powered device might not get the require
+ * current to do a temperature conversion.  If it is enabled parasite powered
+ * devices have a better chance of getting the current required.
+ */
+static int w1_strong_pullup = 1;
+module_param_named(strong_pullup, w1_strong_pullup, int, 0);
 static u8 bad_roms[][9] = {
                                {0xaa, 0x00, 0x4b, 0x46, 0xff, 0xff, 0x0c, 0x10, 0x87},
@@ -192,9 +200,12 @@ static ssize_t w1_therm_read_bin(struct kobject *kobj,
                        int count = 0;
                        unsigned int tm = 750;
+                       /* 750ms strong pullup (or delay) after the convert */
+                       if (w1_strong_pullup)
+                               w1_next_pullup(dev, tm);
                        w1_write_8(dev, W1_CONVERT_TEMP);
-                       msleep(tm);
+                       if (!w1_strong_pullup)
+                               msleep(tm);
                        if (!w1_reset_select_slave(sl)) {