W1: feature, enable hardware strong pullup

Add a strong pullup option to the w1 system.  This supplies extra power
for parasite powered devices.  There is a w1_master_pullup sysfs entry and
enable_pullup module parameter to enable or disable the strong pullup.

The one wire bus requires at a minimum one wire and ground.  The common
wire is used for sending and receiving data as well as supplying power to
devices that are parasite powered of which temperature sensors can be one
example.  The bus must be idle and left high while a temperature
conversion is in progress, in addition the normal pullup resister on
larger networks or even higher temperatures might not supply enough power.
 The pullup resister can't provide too much pullup current, because
devices need to pull the bus down to write a value.  This enables the
strong pullup for supported hardware, which can supply more current when
requested.  Unsupported hardware will just delay with the bus high.

The hardware USB 2490 one wire bus master has a bit on some commands which
will enable the strong pullup as soon as the command finishes executing.
To use strong pullup, call the new w1_next_pullup function to register the
duration.  The next write command will call set_pullup before sending the
data, and reset the duration to zero once it returns.

Switched from simple_strtol to strict_strtol.

Signed-off-by: David Fries <david@fries.net>
Cc: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/w1/w1_int.c b/drivers/w1/w1_int.c
index bd877b24ce42..9d723efdf915 100644
--- a/drivers/w1/w1_int.c
+++ b/drivers/w1/w1_int.c
@@ -31,6 +31,9 @@
 
 static u32 w1_ids = 1;
 
+static int w1_enable_pullup = 1;
+module_param_named(enable_pullup, w1_enable_pullup, int, 0);
+
 static struct w1_master * w1_alloc_dev(u32 id, int slave_count, int slave_ttl,
                                        struct device_driver *driver,
                                        struct device *device)
@@ -59,6 +62,7 @@ static struct w1_master * w1_alloc_dev(u32 id, int slave_count, int slave_ttl,
         dev->initialized        = 0;
         dev->id                 = id;
         dev->slave_ttl          = slave_ttl;
+        dev->enable_pullup      = w1_enable_pullup;
         dev->search_count       = -1; /* continual scan */
 
         /* 1 for w1_process to decrement
@@ -107,6 +111,18 @@ int w1_add_master_device(struct w1_bus_master *master)
                 printk(KERN_ERR "w1_add_master_device: invalid function set\n");
                 return(-EINVAL);
         }
+        /* While it would be electrically possible to make a device that
+         * generated a strong pullup in bit bang mode, only hardare that
+         * controls 1-wire time frames are even expected to support a strong
+         * pullup.  w1_io.c would need to support calling set_pullup before
+         * the last write_bit operation of a w1_write_8 which it currently
+         * doesn't.
+         */
+        if (!master->write_byte && !master->touch_bit && master->set_pullup) {
+                printk(KERN_ERR "w1_add_master_device: set_pullup requires "
+                        "write_byte or touch_bit, disabling\n");
+                master->set_pullup = NULL;
+        }
 
         dev = w1_alloc_dev(w1_ids++, w1_max_slave_count, w1_max_slave_ttl, &w1_master_driver, &w1_master_device);
         if (!dev)