Hi, On Wed, Mar 10, 2021 at 12:20 PM Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx> wrote: > > During suspend/resume usecases and tests, it is common to see issues > such as lockups either in suspend path or resume path because of the > bugs in the corresponding device driver pm handling code. In such cases, > it is important that watchdog is active to make sure that we either > receive a watchdog pretimeout notification or a bite causing reset > instead of a hang causing us to hard reset the machine. > > There are good reasons as to why we need this because: > > * We can have a watchdog pretimeout governor set to panic in which > case we can have a backtrace which would help identify the issue > with the particular driver and cause a normal reboot. > > * Even in case where there is no pretimeout support, a watchdog > bite is still useful because some firmware has debug support to dump > CPU core context on watchdog bite for post-mortem analysis. > > * One more usecase which comes to mind is of warm reboot. In case we > hard reset the target, a cold reboot could be induced resulting in > lose of ddr contents thereby losing all the debug info. > > Currently, the watchdog pm callback just invokes the usual suspend > and resume callback which do not have any special ordering in the > sense that a watchdog can be suspended before the buggy device driver > suspend callback and watchdog resume can happen after the buggy device > driver resume callback. This would mean that the watchdog will not be > active when the buggy driver cause the lockups thereby hanging the > system. So to make sure this doesn't happen, move the watchdog pm to > use late/early system pm callbacks which will ensure that the watchdog > is suspended late and resumed early so that it can catch such issues. > > Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx> > --- > drivers/watchdog/qcom-wdt.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
