1========================================================= 2Converting old watchdog drivers to the watchdog framework 3========================================================= 4 5by Wolfram Sang <w.sang@pengutronix.de> 6 7Before the watchdog framework came into the kernel, every driver had to 8implement the API on its own. Now, as the framework factored out the common 9components, those drivers can be lightened making it a user of the framework. 10This document shall guide you for this task. The necessary steps are described 11as well as things to look out for. 12 13 14Remove the file_operations struct 15--------------------------------- 16 17Old drivers define their own file_operations for actions like open(), write(), 18etc... These are now handled by the framework and just call the driver when 19needed. So, in general, the 'file_operations' struct and assorted functions can 20go. Only very few driver-specific details have to be moved to other functions. 21Here is a overview of the functions and probably needed actions: 22 23- open: Everything dealing with resource management (file-open checks, magic 24 close preparations) can simply go. Device specific stuff needs to go to the 25 driver specific start-function. Note that for some drivers, the start-function 26 also serves as the ping-function. If that is the case and you need start/stop 27 to be balanced (clocks!), you are better off refactoring a separate start-function. 28 29- close: Same hints as for open apply. 30 31- write: Can simply go, all defined behaviour is taken care of by the framework, 32 i.e. ping on write and magic char ('V') handling. 33 34- ioctl: While the driver is allowed to have extensions to the IOCTL interface, 35 the most common ones are handled by the framework, supported by some assistance 36 from the driver: 37 38 WDIOC_GETSUPPORT: 39 Returns the mandatory watchdog_info struct from the driver 40 41 WDIOC_GETSTATUS: 42 Needs the status-callback defined, otherwise returns 0 43 44 WDIOC_GETBOOTSTATUS: 45 Needs the bootstatus member properly set. Make sure it is 0 if you 46 don't have further support! 47 48 WDIOC_SETOPTIONS: 49 No preparations needed 50 51 WDIOC_KEEPALIVE: 52 If wanted, options in watchdog_info need to have WDIOF_KEEPALIVEPING 53 set 54 55 WDIOC_SETTIMEOUT: 56 Options in watchdog_info need to have WDIOF_SETTIMEOUT set 57 and a set_timeout-callback has to be defined. The core will also 58 do limit-checking, if min_timeout and max_timeout in the watchdog 59 device are set. All is optional. 60 61 WDIOC_GETTIMEOUT: 62 No preparations needed 63 64 WDIOC_GETTIMELEFT: 65 It needs get_timeleft() callback to be defined. Otherwise it 66 will return EOPNOTSUPP 67 68 Other IOCTLs can be served using the ioctl-callback. Note that this is mainly 69 intended for porting old drivers; new drivers should not invent private IOCTLs. 70 Private IOCTLs are processed first. When the callback returns with 71 -ENOIOCTLCMD, the IOCTLs of the framework will be tried, too. Any other error 72 is directly given to the user. 73 74Example conversion:: 75 76 -static const struct file_operations s3c2410wdt_fops = { 77 - .owner = THIS_MODULE, 78 - .llseek = no_llseek, 79 - .write = s3c2410wdt_write, 80 - .unlocked_ioctl = s3c2410wdt_ioctl, 81 - .open = s3c2410wdt_open, 82 - .release = s3c2410wdt_release, 83 -}; 84 85Check the functions for device-specific stuff and keep it for later 86refactoring. The rest can go. 87 88 89Remove the miscdevice 90--------------------- 91 92Since the file_operations are gone now, you can also remove the 'struct 93miscdevice'. The framework will create it on watchdog_dev_register() called by 94watchdog_register_device():: 95 96 -static struct miscdevice s3c2410wdt_miscdev = { 97 - .minor = WATCHDOG_MINOR, 98 - .name = "watchdog", 99 - .fops = &s3c2410wdt_fops, 100 -}; 101 102 103Remove obsolete includes and defines 104------------------------------------ 105 106Because of the simplifications, a few defines are probably unused now. Remove 107them. Includes can be removed, too. For example:: 108 109 - #include <linux/fs.h> 110 - #include <linux/miscdevice.h> (if MODULE_ALIAS_MISCDEV is not used) 111 - #include <linux/uaccess.h> (if no custom IOCTLs are used) 112 113 114Add the watchdog operations 115--------------------------- 116 117All possible callbacks are defined in 'struct watchdog_ops'. You can find it 118explained in 'watchdog-kernel-api.txt' in this directory. start(), stop() and 119owner must be set, the rest are optional. You will easily find corresponding 120functions in the old driver. Note that you will now get a pointer to the 121watchdog_device as a parameter to these functions, so you probably have to 122change the function header. Other changes are most likely not needed, because 123here simply happens the direct hardware access. If you have device-specific 124code left from the above steps, it should be refactored into these callbacks. 125 126Here is a simple example:: 127 128 +static struct watchdog_ops s3c2410wdt_ops = { 129 + .owner = THIS_MODULE, 130 + .start = s3c2410wdt_start, 131 + .stop = s3c2410wdt_stop, 132 + .ping = s3c2410wdt_keepalive, 133 + .set_timeout = s3c2410wdt_set_heartbeat, 134 +}; 135 136A typical function-header change looks like:: 137 138 -static void s3c2410wdt_keepalive(void) 139 +static int s3c2410wdt_keepalive(struct watchdog_device *wdd) 140 { 141 ... 142 + 143 + return 0; 144 } 145 146 ... 147 148 - s3c2410wdt_keepalive(); 149 + s3c2410wdt_keepalive(&s3c2410_wdd); 150 151 152Add the watchdog device 153----------------------- 154 155Now we need to create a 'struct watchdog_device' and populate it with the 156necessary information for the framework. The struct is also explained in detail 157in 'watchdog-kernel-api.txt' in this directory. We pass it the mandatory 158watchdog_info struct and the newly created watchdog_ops. Often, old drivers 159have their own record-keeping for things like bootstatus and timeout using 160static variables. Those have to be converted to use the members in 161watchdog_device. Note that the timeout values are unsigned int. Some drivers 162use signed int, so this has to be converted, too. 163 164Here is a simple example for a watchdog device:: 165 166 +static struct watchdog_device s3c2410_wdd = { 167 + .info = &s3c2410_wdt_ident, 168 + .ops = &s3c2410wdt_ops, 169 +}; 170 171 172Handle the 'nowayout' feature 173----------------------------- 174 175A few drivers use nowayout statically, i.e. there is no module parameter for it 176and only CONFIG_WATCHDOG_NOWAYOUT determines if the feature is going to be 177used. This needs to be converted by initializing the status variable of the 178watchdog_device like this:: 179 180 .status = WATCHDOG_NOWAYOUT_INIT_STATUS, 181 182Most drivers, however, also allow runtime configuration of nowayout, usually 183by adding a module parameter. The conversion for this would be something like:: 184 185 watchdog_set_nowayout(&s3c2410_wdd, nowayout); 186 187The module parameter itself needs to stay, everything else related to nowayout 188can go, though. This will likely be some code in open(), close() or write(). 189 190 191Register the watchdog device 192---------------------------- 193 194Replace misc_register(&miscdev) with watchdog_register_device(&watchdog_dev). 195Make sure the return value gets checked and the error message, if present, 196still fits. Also convert the unregister case:: 197 198 - ret = misc_register(&s3c2410wdt_miscdev); 199 + ret = watchdog_register_device(&s3c2410_wdd); 200 201 ... 202 203 - misc_deregister(&s3c2410wdt_miscdev); 204 + watchdog_unregister_device(&s3c2410_wdd); 205 206 207Update the Kconfig-entry 208------------------------ 209 210The entry for the driver now needs to select WATCHDOG_CORE: 211 212 + select WATCHDOG_CORE 213 214 215Create a patch and send it to upstream 216-------------------------------------- 217 218Make sure you understood Documentation/process/submitting-patches.rst and send your patch to 219linux-watchdog@vger.kernel.org. We are looking forward to it :) 220