2 files changed, 20 insertions, 4 deletions

diff --git a/Documentation/w1/slaves/w1_therm b/Documentation/w1/slaves/w1_therm
index 874a8ca93feb..cc62a95e4776 100644
--- a/Documentation/w1/slaves/w1_therm
+++ b/Documentation/w1/slaves/w1_therm
@@ -34,9 +34,16 @@ 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
+strong pullup, 1 to enable autodetection or 2 to force strong pullup.
+In case of autodetection, the driver will use the "READ POWER SUPPLY"
+command to check if there are pariste powered devices on the bus.
+If so, it will activate the master's strong pullup.
+In case the detection of parasite devices using this command fails
+(seems to be the case with some DS18S20) the strong pullup can
+be force-enabled.
+If the strong pullup is enabled, the master's strong pullup will be
+driven when the conversion is taking place, provided the master driver
+does 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
diff --git a/drivers/w1/slaves/w1_therm.c b/drivers/w1/slaves/w1_therm.c
index 5ef583d520fa..c1a702f8c803 100644
--- a/drivers/w1/slaves/w1_therm.c
+++ b/drivers/w1/slaves/w1_therm.c
@@ -41,6 +41,14 @@ MODULE_DESCRIPTION("Driver for 1-wire Dallas network protocol, temperature famil
  * 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.
+ * In case the parasite power-detection is not working (seems to be the case
+ * for some DS18S20) the strong pullup can also be forced, regardless of the
+ * power state of the devices.
+ *
+ * Summary of options:
+ * - strong_pullup = 0  Disable strong pullup completely
+ * - strong_pullup = 1  Enable automatic strong pullup detection
+ * - strong_pullup = 2  Force strong pullup
  */
 static int w1_strong_pullup = 1;
 module_param_named(strong_pullup, w1_strong_pullup, int, 0);
@@ -197,7 +205,8 @@ static ssize_t w1_therm_read(struct device *device,
                                 continue;
 
                         /* 750ms strong pullup (or delay) after the convert */
-                        if (!external_power && w1_strong_pullup)
+                        if (w1_strong_pullup == 2 ||
+                                        (!external_power && w1_strong_pullup))
                                 w1_next_pullup(dev, tm);
 
                         w1_write_8(dev, W1_CONVERT_TEMP);