On Sat, 30 Oct 2021 at 18:14, Guenter Roeck [off-list ref] wrote:

On 10/30/21 7:29 AM, Sam Protsenko wrote:

quoted

On Fri, 29 Oct 2021 at 03:30, Guenter Roeck [off-list ref] wrote:

quoted

On 10/28/21 11:35 AM, Sam Protsenko wrote:

quoted

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@linaro.org>
---
   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