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Subject[PATCH] Introduce an ability to specify microseconds bus scanning intervals in w1 core
DS1990* "iButtons" and compatible RFID card readers commonly found at
physical access control systems are usually attached/generate presence
for as short as 100 ms - hence the tens-to-hundreds milliseconds scan
intervals are required.

Tested on Raspberry Pi model B+ with DS2482-100 bus master,
tens-of-milliseconds intervals are easily achieved without significant
CPU load (and with unknown accuracy), and though I doubt
microseconds-scale intervals are really feasible in terms of practical
use and underlying buses timings, I believe it makes sense to give the
ability of using them to those willing to try.

Signed-off-by: Dmitry Khromov <dk@icelogic.net>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>

drivers/w1/w1.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
---
diff --git a/drivers/w1/w1.c b/drivers/w1/w1.c
index 181f41c..73b4e2d 100644
--- a/drivers/w1/w1.c
+++ b/drivers/w1/w1.c
@@ -46,11 +46,15 @@ MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
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
@@ -317,6 +321,14 @@ static ssize_t w1_master_attribute_show_timeout(struct device *dev, struct devic
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)
{
@@ -543,6 +555,7 @@ static W1_MASTER_ATTR_RO(slave_count, S_IRUGO);
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);
@@ -556,6 +569,7 @@ static struct attribute *w1_master_default_attrs[] = {
&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,
@@ -1108,7 +1122,8 @@ int w1_process(void *data)
/* 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;

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