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w1: enable active pullup for DS2482 by default 

This commit enables the active pullup (APU bit) by default for
the DS2482 1-Wire master.

>From the DS2482 datasheet:
"The APU bit controls whether an active pullup (controlled slew-rate
transistor) or a passive pullup (Rwpu resistor) will be used to drive
a 1-Wire line from low to high. When APU = 0, active pullup is disabled
(resistor mode). Active Pullup should always be selected unless there is
only a single slave on the 1-Wire line."

According to the module author, Ben Gardner:
"It doesn't look like active pullup would cause any hurt if there
is only a single slave."
And my tests with multiple and single slaves on 1-Wire bus
confirms that.

This active pullup can be manually disabled using the introduced
module parameter:
  active_pullup = 0

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Mariusz Bialonczyk 2016-03-29 18:41:38 +02:00 committed by Greg Kroah-Hartman
parent a8ab316ab1
commit f704938c0e
1 changed files with 18 additions and 0 deletions
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18
drivers/w1/masters/ds2482.c
View File

@ -23,6 +23,19 @@
#include "../w1.h"
#include "../w1_int.h"
/**
* Allow the active pullup to be disabled, default is enabled.
*
* Note from the DS2482 datasheet:
* The APU bit controls whether an active pullup (controlled slew-rate
* transistor) or a passive pullup (Rwpu resistor) will be used to drive
* a 1-Wire line from low to high. When APU = 0, active pullup is disabled
* (resistor mode). Active Pullup should always be selected unless there is
* only a single slave on the 1-Wire line.
*/
static int ds2482_active_pullup = 1;
module_param_named(active_pullup, ds2482_active_pullup, int, 0644);
/**
* The DS2482 registers - there are 3 registers that are addressed by a read
* pointer. The read pointer is set by the last command executed.
@ -138,6 +151,9 @@ struct ds2482_data {
*/
static inline u8 ds2482_calculate_config(u8 conf)
{
if (ds2482_active_pullup)
conf |= DS2482_REG_CFG_APU;
return conf | ((~conf & 0x0f) << 4);
}
@ -546,6 +562,8 @@ static int ds2482_remove(struct i2c_client *client)
module_i2c_driver(ds2482_driver);
MODULE_PARM_DESC(active_pullup, "Active pullup (apply to all buses): " \
"0-disable, 1-enable (default)");
MODULE_AUTHOR("Ben Gardner <bgardner@wabtec.com>");
MODULE_DESCRIPTION("DS2482 driver");
MODULE_LICENSE("GPL");