Fix erroneous commit
This commit is contained in:
Wolfgang Denk
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright 2002 Detlev Zundel (dzu@denx.de)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one
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.\"
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.TH WDT_MPC5XXX "Denx specific extensions"
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.SH NAME
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wdt_mpc5xxx \- Watchdog driver
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.SH SYNOPSIS
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.B #include <linux/asm/wdt_mpc5xxx.h>
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.SH DESCRIPTION
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The
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.B wdt_mpc5xxx
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driver implements a character device with major number 10 and minor
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number 130. It is a software abstraction of the hardware watchdog
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with two different APIs. While the driver periodically triggers the
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hardware watchdog, the software can setup independent timeout periods.
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.SH "REGULAR API"
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The regular API provides a facility to setup a watchdog behaviour
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.I shared
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by all processes using the driver. This interface uses read(2),
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write(2) and the first two ioctl(2) calls listed below. The
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parameterless ioctl(2) calls select the operational mode of the
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driver, which can be
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.I open-only
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or
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.I always.
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In open-only mode, the watchdog will not expire if the device file is
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not opened by any process, while in always
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mode the behaviour is independent of the device file being opened.
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Reading from the device file will return an unsigned integer denoting
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the number of seconds left till the watchdog expires. Writing an
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unsigned integer to the device file will set the expiration period in
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seconds. Note that the hardware watchdog will be triggered
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independently with a configurable period. See the section
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CONFIGURATION for details.
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An expiration of the watchdog will trigger a hard-reset of the machine.
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.SH "CHAIN API"
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The second API, which is implemented only through calls to ioctl(2),
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can be used to register configurable
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.I watchdog chains
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from either user or kernel space. A watchdog chain
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is identified by an unsigned integer and can contain up to three
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.I action stages.
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A
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.I time interval
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in seconds and an
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.I action
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is associated with each stage. When the chain is not reset before the
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interval elapses, the associated action is triggered and the chain
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moves on to the next stage.
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A chain can request to kill the registering process if the interval
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elapses. In this case a restarted process can register with the
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driver giving the same identifier and reset the chain. This is the
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main reason why there is no association between chains and processes
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or open device files.
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For a detailed description of the possible chain configurations, see
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the description of the
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.B WDT_REGISTER
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ioctl call.
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Note that when mixing the two interfaces, the second API takes
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precedence. That is, expiry of the interval set by writing to the
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device file while a chain is registered, will not trigger any actions.
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Also note that the default operational mode of the driver,
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i.e. open-only or always can only be configured in the source-code.
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.SH IOCTLS
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.TP
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WDT_OPEN_ONLY
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This parameterless call selects the
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.I open-only
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operational mode of the driver as described above.
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.TP
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WDT_ALWAYS
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Also a parameterless call, this sets the driver to the
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.I always
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operational mode.
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.TP
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WDT_REGISTER
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This and the two following ioctls constitute the
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.I chain interface
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described above. The parameter given to the call is a pointer to a
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structure with the following layout:
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typedef struct wdt_param {
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unsigned chainid;
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unsigned long timer_count[3];
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int action[3];
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int signal;
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} wdt_param_t;
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Each stage is configured with entries in the arrays
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.I timer_count
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and
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.I action.
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The timer_count contains the length of the interval in seconds
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while action contains one of the constants
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.B WDT_ACTION_SIGNAL, WDT_ACTION_KILL,
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.B WDT_ACTION_REBOOT
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and
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.B WDT_ACTION_RESET.
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A timer_count of zero signals the end of the chain.
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The ACTION_SIGNAL will send the configurable signal with number
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.I signal
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to the registering process, while ACTION_KILL signals SIGKILL which
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can not be caught by the registered process.
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ACTION_REBOOT tries a soft reboot and ACTION_RESET
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triggers a hard-reset of the machine.
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When stages of the chain are to be left unused, they should be filled
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with zero entries.
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Note that internally a hard-reset stage is appended as a stop entry
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ensuring a chain will never exceed its stages.
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.TP
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WDT_RESET
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This call resets the chain denoted by the unsigned integer passed to
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it. When reset, a chain will expire beginning with stage zero again.
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.TP
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WDT_UNREGISTER
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As closing the device file will not have any effect on chains, a
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process must unregister a chain if the service is no longer needed.
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This can be done with this ioctl taking an unsigned integer as a
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parameter denoting the chain to be unregistered.
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.SH "IOCTL RESULT VALUES"
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On successful completion, the above calls to ioctl(2) return 0. When
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invalid parameters are provided or an error occurs, a negative value
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will be returned and
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.B errno
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set accordingly. Specifically
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.B "EINVAL, EFAULT, ENOMEM"
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can be returned.
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.SH "KERNEL INTERFACE"
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Modules can also register with the chain API of the watchdog driver.
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For this the three functions
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.B wdt_register_mon_chain, wdt_reset_mon_chain
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and
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.B wdt_unregister_mon_chain
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are exported from the driver. The first function takes one argument,
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namely a pointer to a
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.I wdt_param
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structure. The other two calls take a pointer to an unsigned integer
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as a parameter, namely the chain id of the chain to be reset or
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unregistered.
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.SH CONFIGURATION
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The driver is configurable through parameters passed to the driver
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through the Linux commandline as
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.B "wdt=<opts>".
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Multiple options can be seperated by
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commas, as usual.
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.B timeout:<n>
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will set the expiry period of the regular driver API to <n> seconds.
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.B period:<n>
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sets the period with which the hardware watchdog is triggered to <n>
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jiffies. This usually means 1/100th of a second. The default for the
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MPC5xxx is (1*HZ), resulting in 1 watchdog trigger per second.
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.B off
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will disable the software APIs of the driver but still trigger the
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hardware watchdog as described previously.
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.SH EXAMPLE
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The following code snippet registers a watchdog chain whose first
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stage will expire after 3 seconds and send the SIGUSR1 signal to the
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process. When 5 seconds after this the chain is not reset, the
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machine will do a hard-reset.
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wdt_param_t param;
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/* Setup signal handling */
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signal(SIGUSR1, got_signal);
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param.chainid=823;
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param.timer_count[0]=3;
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param.action[0]=WDT_ACTION_KILL;
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param.signal=SIGUSR1;
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param.timer_count[1]=5;
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param.action[1]=WDT_ACTION_RESET;
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/* Register chain */
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ioctl(fd, WDT_REGISTER, ¶m);
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..
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/* Reset chain */
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ioctl(fd, WDT_RESET, ¶m.chainid);
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.SH FILES
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/dev/watchdog
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