path: root/Documentation
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authorLinus Torvalds <torvalds@linux-foundation.org>2012-05-30 09:59:13 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-30 09:59:13 -0700
commit19ce0a995ff230b364c7329fd488c70e91c171d9 (patch)
treee24fe57a87d16a54cbffd087fb6af2083f7f2ad0 /Documentation
parentMerge branch 'drm-fixes' of git://people.freedesktop.org/~airlied/linux (diff)
parentwatchdog: iTCO_wdt.c: fix printk format warnings (diff)
Merge git://www.linux-watchdog.org/linux-watchdog
Pull second set of watchdog updates from Wim Van Sebroeck: "This changeset contains following changes: * Add support for multiple watchdog devices. We use dynamically allocated device id's for this. * Add locking into the generic watchdog infrastructure. * Add support for dynamically allocated watchdog_device structs so that we can deal with devices that get unbound. * convert following drivers to the generic watchdog framework: sch5627, sch5636 and sp805_wdt. * Add DA9052/53 PMIC watchdog support * Fix printk format warnings for iTCO_wdt.c" * git://www.linux-watchdog.org/linux-watchdog: watchdog: iTCO_wdt.c: fix printk format warnings watchdog: sp805_wdt: Add clk_{un}prepare support watchdog: sp805_wdt: convert to watchdog core hwmon/sch56xx: Depend on watchdog for watchdog core functions watchdog: sch56xx-common: set correct bits in register() Watchdog: DA9052/53 PMIC watchdog support watchdog: sch56xx-common: Add proper ref-counting of watchdog data watchdog: sch56xx: Remove unnecessary checks for register changes watchdog: sch56xx: Use watchdog core watchdog: Add support for dynamically allocated watchdog_device structs watchdog: Add Locking support watchdog: watchdog_dev: Rewrite wrapper code watchdog: use dev_ functions watchdog: create all the proper device files watchdog: Add a flag to indicate the watchdog doesn't reboot things watchdog: Add multiple device support watchdog: watchdog_core.h: make functions extern watchdog: correct the name of the watchdog_core inlude file watchdog: Add watchdog_active() routine watchdog: watchdog_dev: include private header to pickup global symbol prototypes
Diffstat (limited to 'Documentation')
2 files changed, 47 insertions, 1 deletions
diff --git a/Documentation/watchdog/watchdog-kernel-api.txt b/Documentation/watchdog/watchdog-kernel-api.txt
index 25fe4304f2fc..086638f6c82d 100644
--- a/Documentation/watchdog/watchdog-kernel-api.txt
+++ b/Documentation/watchdog/watchdog-kernel-api.txt
@@ -1,6 +1,6 @@
The Linux WatchDog Timer Driver Core kernel API.
-Last reviewed: 16-Mar-2012
+Last reviewed: 22-May-2012
Wim Van Sebroeck <wim@iguana.be>
@@ -39,6 +39,10 @@ watchdog_device structure.
The watchdog device structure looks like this:
struct watchdog_device {
+ int id;
+ struct cdev cdev;
+ struct device *dev;
+ struct device *parent;
const struct watchdog_info *info;
const struct watchdog_ops *ops;
unsigned int bootstatus;
@@ -46,10 +50,20 @@ struct watchdog_device {
unsigned int min_timeout;
unsigned int max_timeout;
void *driver_data;
+ struct mutex lock;
unsigned long status;
It contains following fields:
+* id: set by watchdog_register_device, id 0 is special. It has both a
+ /dev/watchdog0 cdev (dynamic major, minor 0) as well as the old
+ /dev/watchdog miscdev. The id is set automatically when calling
+ watchdog_register_device.
+* cdev: cdev for the dynamic /dev/watchdog<id> device nodes. This
+ field is also populated by watchdog_register_device.
+* dev: device under the watchdog class (created by watchdog_register_device).
+* parent: set this to the parent device (or NULL) before calling
+ watchdog_register_device.
* info: a pointer to a watchdog_info structure. This structure gives some
additional information about the watchdog timer itself. (Like it's unique name)
* ops: a pointer to the list of watchdog operations that the watchdog supports.
@@ -61,6 +75,7 @@ It contains following fields:
* driver_data: a pointer to the drivers private data of a watchdog device.
This data should only be accessed via the watchdog_set_drvdata and
watchdog_get_drvdata routines.
+* lock: Mutex for WatchDog Timer Driver Core internal use only.
* status: this field contains a number of status bits that give extra
information about the status of the device (Like: is the watchdog timer
running/active, is the nowayout bit set, is the device opened via
@@ -78,6 +93,8 @@ struct watchdog_ops {
unsigned int (*status)(struct watchdog_device *);
int (*set_timeout)(struct watchdog_device *, unsigned int);
unsigned int (*get_timeleft)(struct watchdog_device *);
+ void (*ref)(struct watchdog_device *);
+ void (*unref)(struct watchdog_device *);
long (*ioctl)(struct watchdog_device *, unsigned int, unsigned long);
@@ -85,6 +102,21 @@ It is important that you first define the module owner of the watchdog timer
driver's operations. This module owner will be used to lock the module when
the watchdog is active. (This to avoid a system crash when you unload the
module and /dev/watchdog is still open).
+If the watchdog_device struct is dynamically allocated, just locking the module
+is not enough and a driver also needs to define the ref and unref operations to
+ensure the structure holding the watchdog_device does not go away.
+The simplest (and usually sufficient) implementation of this is to:
+1) Add a kref struct to the same structure which is holding the watchdog_device
+2) Define a release callback for the kref which frees the struct holding both
+3) Call kref_init on this kref *before* calling watchdog_register_device()
+4) Define a ref operation calling kref_get on this kref
+5) Define a unref operation calling kref_put on this kref
+6) When it is time to cleanup:
+ * Do not kfree() the struct holding both, the last kref_put will do this!
+ * *After* calling watchdog_unregister_device() call kref_put on the kref
Some operations are mandatory and some are optional. The mandatory operations
* start: this is a pointer to the routine that starts the watchdog timer
@@ -125,6 +157,10 @@ they are supported. These optional routines/operations are:
(Note: the WDIOF_SETTIMEOUT needs to be set in the options field of the
watchdog's info structure).
* get_timeleft: this routines returns the time that's left before a reset.
+* ref: the operation that calls kref_get on the kref of a dynamically
+ allocated watchdog_device struct.
+* unref: the operation that calls kref_put on the kref of a dynamically
+ allocated watchdog_device struct.
* ioctl: if this routine is present then it will be called first before we do
our own internal ioctl call handling. This routine should return -ENOIOCTLCMD
if a command is not supported. The parameters that are passed to the ioctl
@@ -144,6 +180,11 @@ bit-operations. The status bits that are defined are:
(This bit should only be used by the WatchDog Timer Driver Core).
* WDOG_NO_WAY_OUT: this bit stores the nowayout setting for the watchdog.
If this bit is set then the watchdog timer will not be able to stop.
+* WDOG_UNREGISTERED: this bit gets set by the WatchDog Timer Driver Core
+ after calling watchdog_unregister_device, and then checked before calling
+ any watchdog_ops, so that you can be sure that no operations (other then
+ unref) will get called after unregister, even if userspace still holds a
+ reference to /dev/watchdog
To set the WDOG_NO_WAY_OUT status bit (before registering your watchdog
timer device) you can either:
diff --git a/Documentation/watchdog/watchdog-parameters.txt b/Documentation/watchdog/watchdog-parameters.txt
index 17ddd822b456..04fddbacdbde 100644
--- a/Documentation/watchdog/watchdog-parameters.txt
+++ b/Documentation/watchdog/watchdog-parameters.txt
@@ -78,6 +78,11 @@ wd0_timeout: Default watchdog0 timeout in 1/10secs
wd1_timeout: Default watchdog1 timeout in 1/10secs
wd2_timeout: Default watchdog2 timeout in 1/10secs
+timeout: Watchdog timeout in seconds. 2<= timeout <=131, default=2.048s
+nowayout: Watchdog cannot be stopped once started
+ (default=kernel config parameter)
heartbeat: Watchdog heartbeat period in seconds from 1 to 600, default 60