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Commit f704938c authored by Mariusz Bialonczyk's avatar Mariusz Bialonczyk Committed by Greg Kroah-Hartman
Browse files

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: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a8ab316a

drivers/w1/masters/ds2482.c

+18 −0
Original line number Diff line number Diff line
@@ -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");