On Sat, 30 Oct 2021 at 18:14, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> On 10/30/21 7:29 AM, Sam Protsenko wrote:
> > On Fri, 29 Oct 2021 at 03:30, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> >>
> >> On 10/28/21 11:35 AM, Sam Protsenko wrote:
> >>> When "tmr_atboot" module param is set, the watchdog is started in
> >>> driver's probe. In that case, also set WDOG_HW_RUNNING bit to let
> >>> watchdog core driver know it's running. This way wathcdog core can kick
> >>> the watchdog for us (if CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED option is
> >>> enabled), until user space takes control.
> >>>
> >>> Signed-off-by: Sam Protsenko <semen.protsenko@xxxxxxxxxx>
> >>> ---
> >>> drivers/watchdog/s3c2410_wdt.c | 26 +++++++++++++++-----------
> >>> 1 file changed, 15 insertions(+), 11 deletions(-)
> >>>
> >>> diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
> >>> index ca082b1226e3..9af014ff1468 100644
> >>> --- a/drivers/watchdog/s3c2410_wdt.c
> >>> +++ b/drivers/watchdog/s3c2410_wdt.c
> >>> @@ -732,6 +732,21 @@ static int s3c2410wdt_probe(struct platform_device *pdev)
> >>> wdt->wdt_device.bootstatus = s3c2410wdt_get_bootstatus(wdt);
> >>> wdt->wdt_device.parent = dev;
> >>>
> >>> + /*
> >>> + * If "tmr_atboot" param is non-zero, start the watchdog right now. Also
> >>> + * set WDOG_HW_RUNNING bit, so that watchdog core can kick the watchdog.
> >>> + *
> >>> + * If we're not enabling the watchdog, then ensure it is disabled if it
> >>> + * has been left running from the bootloader or other source.
> >>> + */
> >>> + if (tmr_atboot && started == 0) {
> >>> + dev_info(dev, "starting watchdog timer\n");
> >>> + s3c2410wdt_start(&wdt->wdt_device);
> >>> + set_bit(WDOG_HW_RUNNING, &wdt->wdt_device.status);
> >>> + } else if (!tmr_atboot) {
> >>> + s3c2410wdt_stop(&wdt->wdt_device);
> >>> + }
> >>> +
> >>
> >> This doesn't cover the case where the watchdog is already enabled by the BIOS.
> >> In that case, WDOG_HW_RUNNING won't be set, and the watchdog will time out
> >> if the userspace handler is not loaded fast enough. The code should consistently
> >> set WDOG_HW_RUNNING if the watchdog is running.
> >>
> >
> > As I understand, in the case when bootloader started the watchdog, the
> > driver just stops it. You can see it in the code you replied to.
> >
> > } else if (!tmr_atboot) {
> > s3c2410wdt_stop(&wdt->wdt_device);
> >
> > In other words, having "tmr_atboot" module param makes it irrelevant
> > whether bootloader enabled WDT or no.
> >
>
> Sure, but I am concerned about "if (tmr_atboot && started)", which doesn't
> set WDOG_HW_RUNNING with your current code, and I was looking for something
> like
>
> if (tmr_atboot) {
> if (!started) {
> dev_info(dev, "starting watchdog timer\n");
> s3c2410wdt_start(&wdt->wdt_device);
> }
> set_bit(WDOG_HW_RUNNING, &wdt->wdt_device.status);
> } else {
> s3c2410wdt_stop(&wdt->wdt_device);
> }
>
Wow, I really overlooked that case. Nice catch! Not having '} else {'
section is vicious...
Though if started != 0, it means s3c2410wdt_set_heartbeat() failed to
set wdd->timeout, and without that the watchdog core won't be able to
calculate correctly ping interval in watchdog_next_keepalive(), and
WDOG_HW_RUNNING bit won't do much good, right? So I'll probably just
call s3c2410wdt_stop() in that case, to be on the safe side.
Also this 'started' variable name is misleading, I'll convert it to
"bool timeout_ok" while at it.
> Guenter
