On 4/12/21 1:29 AM, Flavio Suligoi wrote: > Hi Guenter, > > ... > >> On 4/9/21 2:34 AM, Flavio Suligoi wrote: >>> The new parameter "start_enabled" starts the watchdog at the same time >>> of the module insertion. >>> This feature is very useful in embedded systems, to avoid cases where >>> the system hangs before reaching userspace. >>> >>> This function can be also enabled in the kernel config, so can be >>> used when the watchdog driver is build as built-in. >>> >>> This parameter involves the "core" section of the watchdog driver; >>> in this way it is common for all the watchdog hardware implementations. >>> >>> Note: to use only for watchdog drivers which doesn't support this >>> parameter by itself. >>> >>> Signed-off-by: Flavio Suligoi <f.suligoi@xxxxxxx> >>> --- >>> Documentation/watchdog/watchdog-parameters.rst | 5 +++++ >>> drivers/watchdog/Kconfig | 14 ++++++++++++++ >>> drivers/watchdog/watchdog_core.c | 12 ++++++++++++ >>> 3 files changed, 31 insertions(+) >>> >>> diff --git a/Documentation/watchdog/watchdog-parameters.rst >> b/Documentation/watchdog/watchdog-parameters.rst >>> index 223c99361a30..623fd064df91 100644 >>> --- a/Documentation/watchdog/watchdog-parameters.rst >>> +++ b/Documentation/watchdog/watchdog-parameters.rst >>> @@ -21,6 +21,11 @@ watchdog core: >>> timeout. Setting this to a non-zero value can be useful to ensure that >>> either userspace comes up properly, or the board gets reset and allows >>> fallback logic in the bootloader to try something else. >>> + start_enabled: >>> + Watchdog is started on module insertion. This option can be also >>> + selected by kernel config (default=kernel config parameter). >>> + Use only for watchdog drivers which doesn't support this parameter >>> + by itself. >> >> Why ? > > There are two drivers with an analogous feature (pnx833x_wdt and > omap_wdt) and it is important not to enable the watchdog twice. > Why ? > Ok, I can substitute the sentence: " Use only for watchdog drivers > which doesn't support this parameter itself." with another one, like: > "If the driver supports this feature by itself, be carefully not to enable > the watchdog twice". > > What do you think? > I am still missing the explanation _why_ it would be important not to enable a watchdog twice. Why does it matter ? What is the difference ? If there is a concern that the start function should not be called on an already running watchdog, the code could check for that and ensure that WDOG_HW_RUNNING is not already set before enabling it. That would probably make sense anyway. But adding a limitation/restriction like the above, which is not enforceable, is not a good idea. How would the common user know if a watchdog is already running (eg because it was started in BIOS/ROMMON) ? Thanks, Guenter
