w1: introduce an ability to specify microseconds bus scanning intervals

Some of 1-Wire devices commonly associated with physical access control
systems are attached/generate presence for as short as 100 ms - hence
the tens-to-hundreds milliseconds scan intervals are required.

Signed-off-by: Dmitry Khromov <[e-mail]>
Acked-by: Evgeniy Polyakov <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/stable/sysfs-bus-w1

···
+What:		/sys/bus/w1/devices/.../w1_master_timeout_us
+Date:		April 2015
+Contact:	Dmitry Khromov <[e-mail]>
+Description:	Bus scanning interval, microseconds component.
+		Some of 1-Wire devices commonly associated with physical access
+		control systems are attached/generate presence for as short as
+		100 ms - hence the tens-to-hundreds milliseconds scan intervals
+		are required.
+		see Documentation/w1/w1.generic for detailed information.
+Users:		any user space application which wants to know bus scanning
+		interval

Documentation/w1/w1.generic

···
 
 w1 master sysfs interface
 ------------------------------------------------------------------
-<xx-xxxxxxxxxxxxx> - a directory for a found device. The format is family-serial
+<xx-xxxxxxxxxxxxx> - A directory for a found device. The format is family-serial
 bus                - (standard) symlink to the w1 bus
 driver             - (standard) symlink to the w1 driver
-w1_master_add      - Manually register a slave device
-w1_master_attempts - the number of times a search was attempted
+w1_master_add      - (rw) manually register a slave device
+w1_master_attempts - (ro) the number of times a search was attempted
 w1_master_max_slave_count
-                   - maximum number of slaves to search for at a time
-w1_master_name     - the name of the device (w1_bus_masterX)
-w1_master_pullup   - 5V strong pullup 0 enabled, 1 disabled
-w1_master_remove   - Manually remove a slave device
-w1_master_search   - the number of searches left to do, -1=continual (default)
+                   - (rw) maximum number of slaves to search for at a time
+w1_master_name     - (ro) the name of the device (w1_bus_masterX)
+w1_master_pullup   - (rw) 5V strong pullup 0 enabled, 1 disabled
+w1_master_remove   - (rw) manually remove a slave device
+w1_master_search   - (rw) the number of searches left to do,
+		     -1=continual (default)
 w1_master_slave_count
-                   - the number of slaves found
-w1_master_slaves   - the names of the slaves, one per line
-w1_master_timeout  - the delay in seconds between searches
+                   - (ro) the number of slaves found
+w1_master_slaves   - (ro) the names of the slaves, one per line
+w1_master_timeout  - (ro) the delay in seconds between searches
+w1_master_timeout_us
+                   - (ro) the delay in microseconds beetwen searches
 
 If you have a w1 bus that never changes (you don't add or remove devices),
 you can set the module parameter search_count to a small positive number
···
 redetect manually removed devices that are present and timeout manually
 added devices that aren't on the bus.
 
+Bus searches occur at an interval, specified as a summ of timeout and
+timeout_us module parameters (either of which may be 0) for as long as
+w1_master_search remains greater than 0 or is -1.  Each search attempt
+decrements w1_master_search by 1 (down to 0) and increments
+w1_master_attempts by 1.
 
 w1 slave sysfs interface
 ------------------------------------------------------------------

drivers/w1/w1.c

···
 MODULE_DESCRIPTION("Driver for 1-wire Dallas network protocol.");
 
 static int w1_timeout = 10;
+static int w1_timeout_us = 0;
 int w1_max_slave_count = 64;
 int w1_max_slave_ttl = 10;
 
 module_param_named(timeout, w1_timeout, int, 0);
 MODULE_PARM_DESC(timeout, "time in seconds between automatic slave searches");
+module_param_named(timeout_us, w1_timeout_us, int, 0);
+MODULE_PARM_DESC(timeout, "time in microseconds between automatic slave"
+		          " searches");
 /* A search stops when w1_max_slave_count devices have been found in that
  * search.  The next search will start over and detect the same set of devices
  * on a static 1-wire bus.  Memory is not allocated based on this number, just
···
 	return count;
 }
 
+static ssize_t w1_master_attribute_show_timeout_us(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	ssize_t count;
+	count = sprintf(buf, "%d\n", w1_timeout_us);
+	return count;
+}
+
 static ssize_t w1_master_attribute_store_max_slave_count(struct device *dev,
 	struct device_attribute *attr, const char *buf, size_t count)
 {
···
 static W1_MASTER_ATTR_RW(max_slave_count, S_IRUGO | S_IWUSR | S_IWGRP);
 static W1_MASTER_ATTR_RO(attempts, S_IRUGO);
 static W1_MASTER_ATTR_RO(timeout, S_IRUGO);
+static W1_MASTER_ATTR_RO(timeout_us, S_IRUGO);
 static W1_MASTER_ATTR_RO(pointer, S_IRUGO);
 static W1_MASTER_ATTR_RW(search, S_IRUGO | S_IWUSR | S_IWGRP);
 static W1_MASTER_ATTR_RW(pullup, S_IRUGO | S_IWUSR | S_IWGRP);
···
 	&w1_master_attribute_max_slave_count.attr,
 	&w1_master_attribute_attempts.attr,
 	&w1_master_attribute_timeout.attr,
+	&w1_master_attribute_timeout_us.attr,
 	&w1_master_attribute_pointer.attr,
 	&w1_master_attribute_search.attr,
 	&w1_master_attribute_pullup.attr,
···
 	/* As long as w1_timeout is only set by a module parameter the sleep
 	 * time can be calculated in jiffies once.
 	 */
-	const unsigned long jtime = msecs_to_jiffies(w1_timeout * 1000);
+	const unsigned long jtime =
+	  usecs_to_jiffies(w1_timeout * 1000000 + w1_timeout_us);
 	/* remainder if it woke up early */
 	unsigned long jremain = 0;