[PATCH v4 1/2] watchdog_core: Add watchdog registration deferral mechanism

[PATCH v4 1/2] watchdog_core: Add watchdog registration deferral mechanism

[Jean-Baptiste Theou]

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 <jtheou@adeneo-embedded.us>
---
Changes in v4:
 - Adjust patch based on Guenter feedbacks on v3

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               | 118 +++++++++++++++++++++----
 include/linux/watchdog.h                       |   3 +
 3 files changed, 110 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..9a35dbb 100644
--- a/drivers/watchdog/watchdog_core.c
+++ b/drivers/watchdog/watchdog_core.c
@@ -43,6 +43,45 @@
 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);
+			break;
+		}
+	}
+}
+
 static void watchdog_check_min_max_timeout(struct watchdog_device *wdd)
 {
 	/*
@@ -98,17 +137,7 @@ 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 +193,33 @@ 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 +235,43 @@ 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;
+
+		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 +288,7 @@ static int __init watchdog_init(void)
 		return err;
 	}
 
+	watchdog_deferred_registration();
 	return 0;
 }
 
@@ -217,7 +299,7 @@ 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 <alan@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

[PATCH v4 2/2] gpio_wdt: Add option for early registration

[Jean-Baptiste Theou]

In some situation, mainly when it's not possible to disable a
watchdog, you may want the watchdog driver to be started as soon
as possible.

Adding GPIO_WATCHDOG_ARCH_INITCALL to raise initcall from
module_init to arch_initcall.

This patch require watchdog registration deferral mechanism

Signed-off-by: Jean-Baptiste Theou <jtheou@adeneo-embedded.us>
---
Changes in v4:
 - Fix symbol
 - Add empty line

Changes in v3:
 - Simplify changes, since the modification is for built-in only


 drivers/watchdog/Kconfig    | 12 ++++++++++++
 drivers/watchdog/gpio_wdt.c |  9 +++++++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index e5e7c55..7a5c912 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -1,3 +1,4 @@
+
 #
 # Watchdog device configuration
 #
@@ -104,6 +105,17 @@ config GPIO_WATCHDOG
 	  If you say yes here you get support for watchdog device
 	  controlled through GPIO-line.
 
+config GPIO_WATCHDOG_ARCH_INITCALL
+	bool "Register the watchdog as early as possible"
+	depends on GPIO_WATCHDOG=y
+	help
+	  In some situations, the default initcall level (module_init)
+	  in not early enough in the boot process to avoid the watchdog
+	  to be triggered.
+	  If you say yes here, the initcall level would be raised to
+	  arch_initcall.
+	  If in doubt, say N.
+
 config MENF21BMC_WATCHDOG
 	tristate "MEN 14F021P00 BMC Watchdog"
 	depends on MFD_MENF21BMC
diff --git a/drivers/watchdog/gpio_wdt.c b/drivers/watchdog/gpio_wdt.c
index cbc313d..1687cc2 100644
--- a/drivers/watchdog/gpio_wdt.c
+++ b/drivers/watchdog/gpio_wdt.c
@@ -267,7 +267,16 @@ static struct platform_driver gpio_wdt_driver = {
 	.probe	= gpio_wdt_probe,
 	.remove	= gpio_wdt_remove,
 };
+
+#ifdef CONFIG_GPIO_WATCHDOG_ARCH_INITCALL
+static int __init gpio_wdt_init(void)
+{
+	return platform_driver_register(&gpio_wdt_driver);
+}
+arch_initcall(gpio_wdt_init);
+#else
 module_platform_driver(gpio_wdt_driver);
+#endif
 
 MODULE_AUTHOR("Alexander Shiyan <shc_work@mail.ru>");
 MODULE_DESCRIPTION("GPIO Watchdog");
-- 
2.4.2

Re: [PATCH v4 1/2] watchdog_core: Add watchdog registration deferral mechanism

[Guenter Roeck]

On 06/06/2015 03:25 PM, Jean-Baptiste Theou wrote:
> 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 <jtheou@adeneo-embedded.us>
> ---
> Changes in v4:
>   - Adjust patch based on Guenter feedbacks on v3
>

You still have lines with > 80 columns, primarily because of very long
variable names. I would suggest to pick shorter names - there is no
technical reason for variables named watchdog_deferred_registration_XXX,
and I don't see why we should have checkpatch warnings just because
of long variable names.

Also, multi-line alignment is still not correct.
I would suggest to run the patch through checkpatch --strict.

Thanks,
Guenter

Re: [PATCH v4 1/2] watchdog_core: Add watchdog registration deferral mechanism

[Jean-Baptiste Theou]

Indeed, it make sense.
I will fix this on v5.

Thanks a lot for your valuable feedbacks on this patch.

JB

On Mon, 8 Jun 2015 12:35:11 -0700
Guenter Roeck <linux@roeck-us.net> wrote:

> On 06/06/2015 03:25 PM, Jean-Baptiste Theou wrote:
> > 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 <jtheou@adeneo-embedded.us>
> > ---
> > Changes in v4:
> >   - Adjust patch based on Guenter feedbacks on v3
> >
> 
> You still have lines with > 80 columns, primarily because of very long
> variable names. I would suggest to pick shorter names - there is no
> technical reason for variables named watchdog_deferred_registration_XXX,
> and I don't see why we should have checkpatch warnings just because
> of long variable names.
> 
> Also, multi-line alignment is still not correct.
> I would suggest to run the patch through checkpatch --strict.
> 
> Thanks,
> Guenter
> 


-- 
Jean-Baptiste Theou <jtheou@adeneo-embedded.us>