On 9/19/19 1:38 AM, Krzysztof Kozlowski wrote:
On Thu, 19 Sep 2019 at 09:40, Suniel Mahesh <sunil.m@xxxxxxxxxxxx> wrote:Hi, I am working on one of the Samsung based S3C2440A chipset based target . I have couple of questions and I request someone to shed some light on these: (Thank you) The watchdog driver in linux, looks like, it just configured WDT but didn't start it (code snippet included below). May i know the reasson why WDT is not started ? Is it because u-boot already started WDT, implies it is not required to do the same once we jump into linux ? or is there any specific reason ? drivers/watchdog/s3c2410_wdt.c (line 53 and lines 616 - 625) #define S3C2410_WATCHDOG_ATBOOT (0) .... static int tmr_atboot = S3C2410_WATCHDOG_ATBOOT; ... ... if (tmr_atboot && started == 0) { dev_info(dev, "starting watchdog timer\n"); s3c2410wdt_start(&wdt->wdt_device); } else if (!tmr_atboot) { /* if we're not enabling the watchdog, then ensure it is * disabled if it has been left running from the bootloader * or other source */ s3c2410wdt_stop(&wdt->wdt_device); } ... ... Tried to start WDT in linux by assigning value 1 to S3C2410_WATCHDOG_ATBOOT. The target resets. please comment.I think watchdog should not start during boot before user-space is brought up. Otherwise who will ping it? Usually watchdog is started by opening the watchdog device by user-space. If you need it to be running without user-space, there are special flags for this (see WDOG_HW_RUNNING and others).
That is not entirely correct. There are use cases where the watchdog is started on purpose and userspace has to open it within a specified period of time to prevent the system from rebooting. Presumably this is what the current driver tries to implement. WDOG_HW_RUNNING was added to the core after the driver was written, so it is not surprising that the driver does not support it. Patches welcome. Thanks, Guenter
