diff options
| -rw-r--r-- | Documentation/w1/slaves/w1_therm | 13 | ||||
| -rw-r--r-- | drivers/w1/slaves/w1_therm.c | 11 |
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); |