Re: [PATCHv2] rtc: pcf2127: handle boot-enabled watchdog feature

["Martin Hundebøll" <martin@geanix.com>]

On 6 October 2019 16.29.45 CEST, Guenter Roeck <linux@roeck-us.net> wrote:
>On 10/6/19 2:07 AM, Bruno Thomsen wrote:
>> Hi Martin,
>> 
>> Den tor. 3. okt. 2019 kl. 15.33 skrev Martin Hundebøll
><martin@geanix.com>:
>>>
>>> Linux should handle when the pcf2127 watchdog feature is enabled by
>the
>>> bootloader. This is done by checking the watchdog timer value during
>>> init, and set the WDOG_HW_RUNNING flag if the value differs from
>zero.
>>>
>>> Signed-off-by: Martin Hundebøll <martin@geanix.com>
>>> ---
>>>
>>> Change since v1:
>>>   * remove setting of WDOG_HW_RUNNING in pcf2127_wdt_start()
>>>
>>>   drivers/rtc/rtc-pcf2127.c | 12 +++++++++++-
>>>   1 file changed, 11 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
>>> index cb3472f..4229915 100644
>>> --- a/drivers/rtc/rtc-pcf2127.c
>>> +++ b/drivers/rtc/rtc-pcf2127.c
>>> @@ -420,6 +420,7 @@ static int pcf2127_probe(struct device *dev,
>struct regmap *regmap,
>>>                          const char *name, bool has_nvmem)
>>>   {
>>>          struct pcf2127 *pcf2127;
>>> +       u32 wdd_timeout;
>>>          int ret = 0;
>>>
>>>          dev_dbg(dev, "%s\n", __func__);
>>> @@ -462,7 +463,6 @@ static int pcf2127_probe(struct device *dev,
>struct regmap *regmap,
>>>          /*
>>>           * Watchdog timer enabled and reset pin /RST activated when
>timed out.
>>>           * Select 1Hz clock source for watchdog timer.
>>> -        * Timer is not started until WD_VAL is loaded with a valid
>value.
>> 
>> Your patch does not change the fact that the watchdog timer is first
>> started after loading a
>> valid value into WD_VAL register. This driver can be used perfectly
>> fine without enabling the
>> watchdog feature from userspace. If someone chooses to reboot without
>> stopping the watchdog
>> it is of course expected to still run on next boot (e.g. device
>probe).
>> 
>>> +       /* Test if watchdog timer is started by bootloader */
>>> +       ret = regmap_read(pcf2127->regmap, PCF2127_REG_WD_VAL,
>&wdd_timeout);
>>> +       if (ret) {
>>> +               dev_err(dev, "%s: watchdog value (wd_wal) failed\n",
>__func__);
>>> +               return ret;
>>> +       }
>>> +
>>> +       if (wdd_timeout)
>>> +               set_bit(WDOG_HW_RUNNING, &pcf2127->wdd.status);
>>> +
>> 
>> I do not agree that this should be the default setting as
>> WDOG_HW_RUNNING bit causes
>> watchdog core to kick watchdog until userland takes over, e.g. you
>> have just broken the
>> chain-of-monitoring in the embedded Linux device:
>> 
>> Hardware watchdog -> systemd -> daemon(s) / application(s)
>> 
>> At this point in time you only know that u-boot / barebox can load
>and
>> start the kernel with
>> a device tree blob.
>> 
>> What if mounting of rootfs fails?
>> What if systemd fails to start?
>> 
>> When doing a reboot due to ex. firmware upgrade, systemd will keep
>> kicking the watchdog
>> until the last sec before restart handler is called and the hardware
>> watchdog should not be
>> touched before systemd is in control of the system again.
>> 
> > Bruno
> >
>
>This should not be decided on driver level. The intended means to
>enforce
>an initial timeout would be to set CONFIG_WATCHDOG_OPEN_TIMEOUT, or to
>use
>the open_timeout kernel parameter.

That, and WATCHDOG_HANDLE_BOOT_ENABLED

// Martin

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