[ 3.5.y.z extended stable ] Patch "pps: Add pps_lookup_dev() function" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Tue Feb 26 16:14:17 UTC 2013

This is a note to let you know that I have just added a patch titled

    pps: Add pps_lookup_dev() function

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From 21a63214b568039fa40386a16a4ba078ccbcd807 Mon Sep 17 00:00:00 2001
From: George Spelvin <linux at horizon.com>
Date: Sun, 10 Feb 2013 04:08:32 -0500
Subject: [PATCH] pps: Add pps_lookup_dev() function

commit 513b032c98b4b9414aa4e9b4a315cb1bf0380101 upstream.

The PPS serial line discipline wants to attach a PPS device to a tty
without changing the tty code to add a struct pps_device * pointer.

Since the number of PPS devices in a typical system is generally very low
(n=1 is by far the most common), it's practical to search the entire list
of allocated pps devices.  (We capture the timestamp before the lookup,
so the timing isn't affected.)

It is a bit ugly that this function, which is part of the in-kernel
PPS API, has to be in pps.c as opposed to kapi,c, but that's not
something that affects users.

Signed-off-by: George Spelvin <linux at horizon.com>
Acked-by: Rodolfo Giometti <giometti at enneenne.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 drivers/pps/pps.c          | 33 +++++++++++++++++++++++++++++++++
 include/linux/pps_kernel.h | 17 ++++++++++++++---
 2 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
index 98fbe62..c50a556 100644
--- a/drivers/pps/pps.c
+++ b/drivers/pps/pps.c
@@ -350,11 +350,44 @@ free_idr:

 void pps_unregister_cdev(struct pps_device *pps)
+	pps->lookup_cookie = NULL;
 	device_destroy(pps_class, pps->dev->devt);

+ * Look up a pps device by magic cookie.
+ * The cookie is usually a pointer to some enclosing device, but this
+ * code doesn't care; you should never be dereferencing it.
+ *
+ * This is a bit of a kludge that is currently used only by the PPS
+ * serial line discipline.  It may need to be tweaked when a second user
+ * is found.
+ *
+ * There is no function interface for setting the lookup_cookie field.
+ * It's initialized to NULL when the pps device is created, and if a
+ * client wants to use it, just fill it in afterward.
+ *
+ * The cookie is automatically set to NULL in pps_unregister_source()
+ * so that it will not be used again, even if the pps device cannot
+ * be removed from the idr due to pending references holding the minor
+ * number in use.
+ */
+struct pps_device *pps_lookup_dev(void const *cookie)
+	struct pps_device *pps;
+	unsigned id;
+	rcu_read_lock();
+	idr_for_each_entry(&pps_idr, pps, id)
+		if (cookie == pps->lookup_cookie)
+			break;
+	rcu_read_unlock();
+	return pps;
  * Module stuff

diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h
index 9404854..ce2ab3d 100644
--- a/include/linux/pps_kernel.h
+++ b/include/linux/pps_kernel.h
@@ -43,7 +43,7 @@ struct pps_source_info {
 			int event, void *data);	/* PPS echo function */

 	struct module *owner;
-	struct device *dev;
+	struct device *dev;		/* Parent device for device_create */

 struct pps_event_time {
@@ -69,6 +69,7 @@ struct pps_device {
 	wait_queue_head_t queue;		/* PPS event queue */

 	unsigned int id;			/* PPS source unique ID */
+	void const *lookup_cookie;		/* pps_lookup_dev only */
 	struct cdev cdev;
 	struct device *dev;
 	struct fasync_struct *async_queue;	/* fasync method */
@@ -82,16 +83,26 @@ struct pps_device {
 extern struct device_attribute pps_attrs[];

+ * Internal functions.
+ *
+ * These are not actually part of the exported API, but this is a
+ * convenient header file to put them in.
+ */
+extern int pps_register_cdev(struct pps_device *pps);
+extern void pps_unregister_cdev(struct pps_device *pps);
  * Exported functions

 extern struct pps_device *pps_register_source(
 		struct pps_source_info *info, int default_params);
 extern void pps_unregister_source(struct pps_device *pps);
-extern int pps_register_cdev(struct pps_device *pps);
-extern void pps_unregister_cdev(struct pps_device *pps);
 extern void pps_event(struct pps_device *pps,
 		struct pps_event_time *ts, int event, void *data);
+/* Look up a pps device by magic cookie */
+struct pps_device *pps_lookup_dev(void const *cookie);

 static inline void timespec_to_pps_ktime(struct pps_ktime *kt,
 		struct timespec ts)

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