W1: feature, w1_therm.c use strong pullup and documentation

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>

1 files changed, 13 insertions, 2 deletions

diff --git a/drivers/w1/slaves/w1_therm.c b/drivers/w1/slaves/w1_therm.c
index fb28acaeed6c..e87f464a6fb0 100644
--- a/drivers/w1/slaves/w1_therm.c
+++ b/drivers/w1/slaves/w1_therm.c
@@ -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)) {