w1: enable active pullup for DS2482 by default (f704938c) · Commits · 戴 / test

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>

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");

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