path: root/Documentation
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authorWolfram Sang <w.sang@pengutronix.de>2011-09-26 15:40:13 +0200
committerWim Van Sebroeck <wim@iguana.be>2011-11-05 21:25:16 +0100
commit74cd4c67392c1cee0499ba0977ec843252c7af28 (patch)
tree1248b9020720ea88c8e24a675ffe75bd317bc272 /Documentation
parentdeb9197b7031b8f4ed311dc47a14363da4458544 (diff)
Documentation: watchdog: add guide how to convert drivers to new framework
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de> Cc: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Diffstat (limited to 'Documentation')
1 files changed, 195 insertions, 0 deletions
diff --git a/Documentation/watchdog/convert_drivers_to_kernel_api.txt b/Documentation/watchdog/convert_drivers_to_kernel_api.txt
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+Converting old watchdog drivers to the watchdog framework
+by Wolfram Sang <w.sang@pengutronix.de>
+Before the watchdog framework came into the kernel, every driver had to
+implement the API on its own. Now, as the framework factored out the common
+components, those drivers can be lightened making it a user of the framework.
+This document shall guide you for this task. The necessary steps are described
+as well as things to look out for.
+Remove the file_operations struct
+Old drivers define their own file_operations for actions like open(), write(),
+etc... These are now handled by the framework and just call the driver when
+needed. So, in general, the 'file_operations' struct and assorted functions can
+go. Only very few driver-specific details have to be moved to other functions.
+Here is a overview of the functions and probably needed actions:
+- open: Everything dealing with resource management (file-open checks, magic
+ close preparations) can simply go. Device specific stuff needs to go to the
+ driver specific start-function. Note that for some drivers, the start-function
+ also serves as the ping-function. If that is the case and you need start/stop
+ to be balanced (clocks!), you are better off refactoring a separate start-function.
+- close: Same hints as for open apply.
+- write: Can simply go, all defined behaviour is taken care of by the framework,
+ i.e. ping on write and magic char ('V') handling.
+- ioctl: While the driver is allowed to have extensions to the IOCTL interface,
+ the most common ones are handled by the framework, supported by some assistance
+ from the driver:
+ Returns the mandatory watchdog_info struct from the driver
+ Needs the status-callback defined, otherwise returns 0
+ Needs the bootstatus member properly set. Make sure it is 0 if you
+ don't have further support!
+ No preparations needed
+ If wanted, options in watchdog_info need to have WDIOF_KEEPALIVEPING
+ set
+ Options in watchdog_info need to have WDIOF_SETTIMEOUT set
+ and a set_timeout-callback has to be defined. The core will also
+ do limit-checking, if min_timeout and max_timeout in the watchdog
+ device are set. All is optional.
+ No preparations needed
+ Other IOCTLs can be served using the ioctl-callback. Note that this is mainly
+ intended for porting old drivers; new drivers should not invent private IOCTLs.
+ Private IOCTLs are processed first. When the callback returns with
+ -ENOIOCTLCMD, the IOCTLs of the framework will be tried, too. Any other error
+ is directly given to the user.
+Example conversion:
+-static const struct file_operations s3c2410wdt_fops = {
+- .owner = THIS_MODULE,
+- .llseek = no_llseek,
+- .write = s3c2410wdt_write,
+- .unlocked_ioctl = s3c2410wdt_ioctl,
+- .open = s3c2410wdt_open,
+- .release = s3c2410wdt_release,
+Check the functions for device-specific stuff and keep it for later
+refactoring. The rest can go.
+Remove the miscdevice
+Since the file_operations are gone now, you can also remove the 'struct
+miscdevice'. The framework will create it on watchdog_dev_register() called by
+-static struct miscdevice s3c2410wdt_miscdev = {
+- .minor = WATCHDOG_MINOR,
+- .name = "watchdog",
+- .fops = &s3c2410wdt_fops,
+Remove obsolete includes and defines
+Because of the simplifications, a few defines are probably unused now. Remove
+them. Includes can be removed, too. For example:
+- #include <linux/fs.h>
+- #include <linux/miscdevice.h> (if MODULE_ALIAS_MISCDEV is not used)
+- #include <linux/uaccess.h> (if no custom IOCTLs are used)
+Add the watchdog operations
+All possible callbacks are defined in 'struct watchdog_ops'. You can find it
+explained in 'watchdog-kernel-api.txt' in this directory. start(), stop() and
+owner must be set, the rest are optional. You will easily find corresponding
+functions in the old driver. Note that you will now get a pointer to the
+watchdog_device as a parameter to these functions, so you probably have to
+change the function header. Other changes are most likely not needed, because
+here simply happens the direct hardware access. If you have device-specific
+code left from the above steps, it should be refactored into these callbacks.
+Here is a simple example:
++static struct watchdog_ops s3c2410wdt_ops = {
++ .owner = THIS_MODULE,
++ .start = s3c2410wdt_start,
++ .stop = s3c2410wdt_stop,
++ .ping = s3c2410wdt_keepalive,
++ .set_timeout = s3c2410wdt_set_heartbeat,
+A typical function-header change looks like:
+-static void s3c2410wdt_keepalive(void)
++static int s3c2410wdt_keepalive(struct watchdog_device *wdd)
+ {
++ return 0;
+ }
+- s3c2410wdt_keepalive();
++ s3c2410wdt_keepalive(&s3c2410_wdd);
+Add the watchdog device
+Now we need to create a 'struct watchdog_device' and populate it with the
+necessary information for the framework. The struct is also explained in detail
+in 'watchdog-kernel-api.txt' in this directory. We pass it the mandatory
+watchdog_info struct and the newly created watchdog_ops. Often, old drivers
+have their own record-keeping for things like bootstatus and timeout using
+static variables. Those have to be converted to use the members in
+watchdog_device. Note that the timeout values are unsigned int. Some drivers
+use signed int, so this has to be converted, too.
+Here is a simple example for a watchdog device:
++static struct watchdog_device s3c2410_wdd = {
++ .info = &s3c2410_wdt_ident,
++ .ops = &s3c2410wdt_ops,
+Register the watchdog device
+Replace misc_register(&miscdev) with watchdog_register_device(&watchdog_dev).
+Make sure the return value gets checked and the error message, if present,
+still fits. Also convert the unregister case.
+- ret = misc_register(&s3c2410wdt_miscdev);
++ ret = watchdog_register_device(&s3c2410_wdd);
+- misc_deregister(&s3c2410wdt_miscdev);
++ watchdog_unregister_device(&s3c2410_wdd);
+Update the Kconfig-entry
+The entry for the driver now needs to select WATCHDOG_CORE:
+Create a patch and send it to upstream
+Make sure you understood Documentation/SubmittingPatches and send your patch to
+linux-watchdog@vger.kernel.org. We are looking forward to it :)