[PATCH] Introduce an ability to specify microseconds bus scanning intervals in w1 core

[Dmitry Khromov]

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@xxxxxxxxxxxx>
Acked-by: Evgeniy Polyakov <zbr@xxxxxxxxxxx>

 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@xxxxxxxxxxx>");
 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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