Currently, watchdog subsystem require the misc subsystem to
register a watchdog. This may not be the case in case of an
early registration of a watchdog, which can be required when
the watchdog cannot be disabled.
This patch introduces a deferral mechanism to remove this requirement.
Signed-off-by: Jean-Baptiste Theou <jth...@adeneo-embedded.us>
---
Changes in v3:
- Adjust patch based on Guenter feedbacks
- Fix watchdog_deferred_registration_del
- Fix typos
Documentation/watchdog/watchdog-kernel-api.txt | 7 ++
drivers/watchdog/watchdog_core.c | 114 +++++++++++++++++++++----
include/linux/watchdog.h | 3 +
3 files changed, 106 insertions(+), 18 deletions(-)
diff --git a/Documentation/watchdog/watchdog-kernel-api.txt
b/Documentation/watchdog/watchdog-kernel-api.txt
index a0438f3..e83518c 100644
--- a/Documentation/watchdog/watchdog-kernel-api.txt
+++ b/Documentation/watchdog/watchdog-kernel-api.txt
@@ -36,6 +36,10 @@ The watchdog_unregister_device routine deregisters a
registered watchdog timer
device. The parameter of this routine is the pointer to the registered
watchdog_device structure.
+The watchdog subsystem includes an registration deferral mechanism,
+which allows you to register an watchdog as early as you wish during
+the boot process.
+
The watchdog device structure looks like this:
struct watchdog_device {
@@ -52,6 +56,7 @@ struct watchdog_device {
void *driver_data;
struct mutex lock;
unsigned long status;
+ struct list_head deferred_registration;
};
It contains following fields:
@@ -80,6 +85,8 @@ It contains following fields:
information about the status of the device (Like: is the watchdog timer
running/active, is the nowayout bit set, is the device opened via
the /dev/watchdog interface or not, ...).
+* deferred_registration: entry in deferred_registration_list which is used to
+ register early initialized watchdogs.
The list of watchdog operations is defined as:
diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
index cec9b55..7dba8d9 100644
--- a/drivers/watchdog/watchdog_core.c
+++ b/drivers/watchdog/watchdog_core.c
@@ -43,6 +43,43 @@
static DEFINE_IDA(watchdog_ida);
static struct class *watchdog_class;
+/*
+ * Deferred Registration infrastructure.
+ *
+ * Sometimes watchdog drivers needs to be loaded as soon as possible,
+ * for example when it's impossible to disable it. To do so,
+ * raising the initcall level of the watchdog driver is a solution.
+ * But in such case, the miscdev is maybe not ready (subsys_initcall), and
+ * watchdog_core need miscdev to register the watchdog as a char device.
+ *
+ * The deferred registration infrastructure offer a way for the watchdog
+ * subsystem to register a watchdog properly, even before miscdev is ready.
+ */
+
+static DEFINE_MUTEX(watchdog_deferred_registration_mutex);
+static LIST_HEAD(watchdog_deferred_registration_pending_list);
+static bool watchdog_deferred_registration_done;
+
+static int watchdog_deferred_registration_add(struct watchdog_device *wdd)
+{
+ list_add_tail(&wdd->deferred_registration,
+ &watchdog_deferred_registration_pending_list);
+ return 0;
+}
+
+static void watchdog_deferred_registration_del(struct watchdog_device *wdd)
+{
+ struct list_head *p, *n;
+ struct watchdog_device *wdd_tmp;
+
+ list_for_each_safe(p, n, &watchdog_deferred_registration_pending_list) {
+ wdd_tmp = list_entry(p, struct watchdog_device,
+ deferred_registration);
+ if (wdd_tmp == wdd)
+ list_del(&wdd_tmp->deferred_registration);
+ }
+}
+
static void watchdog_check_min_max_timeout(struct watchdog_device *wdd)
{
/*
@@ -98,17 +135,7 @@ int watchdog_init_timeout(struct watchdog_device *wdd,
}
EXPORT_SYMBOL_GPL(watchdog_init_timeout);
-/**
- * watchdog_register_device() - register a watchdog device
- * @wdd: watchdog device
- *
- * Register a watchdog device with the kernel so that the
- * watchdog timer can be accessed from userspace.
- *
- * A zero is returned on success and a negative errno code for
- * failure.
- */
-int watchdog_register_device(struct watchdog_device *wdd)
+static int __watchdog_register_device(struct watchdog_device *wdd)
{
int ret, id, devno;
@@ -164,16 +191,33 @@ int watchdog_register_device(struct watchdog_device *wdd)
return 0;
}
-EXPORT_SYMBOL_GPL(watchdog_register_device);
/**
- * watchdog_unregister_device() - unregister a watchdog device
- * @wdd: watchdog device to unregister
+ * watchdog_register_device() - register a watchdog device
+ * @wdd: watchdog device
*
- * Unregister a watchdog device that was previously successfully
- * registered with watchdog_register_device().
+ * Register a watchdog device with the kernel so that the
+ * watchdog timer can be accessed from userspace.
+ *
+ * A zero is returned on success and a negative errno code for
+ * failure.
*/
-void watchdog_unregister_device(struct watchdog_device *wdd)
+
+int watchdog_register_device(struct watchdog_device *wdd)
+{
+ int ret;
+
+ mutex_lock(&watchdog_deferred_registration_mutex);
+ if (watchdog_deferred_registration_done)
+ ret = __watchdog_register_device(wdd);
+ else
+ ret = watchdog_deferred_registration_add(wdd);
+ mutex_unlock(&watchdog_deferred_registration_mutex);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(watchdog_register_device);
+
+static void __watchdog_unregister_device(struct watchdog_device *wdd)
{
int ret;
int devno;
@@ -189,8 +233,41 @@ void watchdog_unregister_device(struct watchdog_device
*wdd)
ida_simple_remove(&watchdog_ida, wdd->id);
wdd->dev = NULL;
}
+
+/**
+ * watchdog_unregister_device() - unregister a watchdog device
+ * @wdd: watchdog device to unregister
+ *
+ * Unregister a watchdog device that was previously successfully
+ * registered with watchdog_register_device().
+ */
+
+void watchdog_unregister_device(struct watchdog_device *wdd)
+{
+ mutex_lock(&watchdog_deferred_registration_mutex);
+ if (watchdog_deferred_registration_done)
+ __watchdog_unregister_device(wdd);
+ else
+ watchdog_deferred_registration_del(wdd);
+ mutex_unlock(&watchdog_deferred_registration_mutex);
+}
+
EXPORT_SYMBOL_GPL(watchdog_unregister_device);
+static int __init watchdog_deferred_registration(void)
+{
+ mutex_lock(&watchdog_deferred_registration_mutex);
+ watchdog_deferred_registration_done = true;
+ while (!list_empty(&watchdog_deferred_registration_pending_list)) {
+ struct watchdog_device *wdd =
list_first_entry(&watchdog_deferred_registration_pending_list,
+ struct
watchdog_device, deferred_registration);
+ list_del(&wdd->deferred_registration);
+ __watchdog_register_device(wdd);
+ }
+ mutex_unlock(&watchdog_deferred_registration_mutex);
+ return 0;
+}
+
static int __init watchdog_init(void)
{
int err;
@@ -207,6 +284,7 @@ static int __init watchdog_init(void)
return err;
}
+ watchdog_deferred_registration();
return 0;
}
@@ -217,7 +295,7 @@ static void __exit watchdog_exit(void)
ida_destroy(&watchdog_ida);
}
-subsys_initcall(watchdog_init);
+subsys_initcall_sync(watchdog_init);
module_exit(watchdog_exit);
MODULE_AUTHOR("Alan Cox <a...@lxorguk.ukuu.org.uk>");
diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
index a746bf5..f9bb943 100644
--- a/include/linux/watchdog.h
+++ b/include/linux/watchdog.h
@@ -65,6 +65,8 @@ struct watchdog_ops {
* @driver-data:Pointer to the drivers private data.
* @lock: Lock for watchdog core internal use only.
* @status: Field that contains the devices internal status bits.
+ * @deferred_registration: entry in deferred_registration_list which is used to
+ * register early initialized watchdogs.
*
* The watchdog_device structure contains all information about a
* watchdog timer device.
@@ -95,6 +97,7 @@ struct watchdog_device {
#define WDOG_ALLOW_RELEASE 2 /* Did we receive the magic char ? */
#define WDOG_NO_WAY_OUT 3 /* Is 'nowayout' feature set ?
*/
#define WDOG_UNREGISTERED 4 /* Has the device been unregistered */
+ struct list_head deferred_registration;
};
#define WATCHDOG_NOWAYOUT IS_BUILTIN(CONFIG_WATCHDOG_NOWAYOUT)
--
2.4.2
--
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