[PATCH 1/2] driver/aspeed-wdt: fix pretimeout for counting down logic

[Heyi Guo]

Really sorry for this mail and previous noisy mails; my thunderbird 
client must be misconfigured to send out mail for command + s shortcut 
when I wanted to save draft...

Heyi

On 2025/2/19 11:40, Heyi Guo wrote:
> Hi Guenter,
>
> Thanks for your comments.
>
> On 2025/2/18 13:33, Guenter Roeck wrote:
> > On 2/17/25 19:16, Heyi Guo wrote:
> >> Aspeed watchdog uses counting down logic, so the value set to register
> >> should be the value of subtracting pretimeout from total timeout.
> >>
> >> Fixes: 9ec0b7e06835 ("watchdog: aspeed: Enable pre-timeout interrupt")
> >>
> >> Signed-off-by: Heyi Guo <guoheyi at linux.alibaba.com>
> >>
> >> Cc: Wim Van Sebroeck <wim at linux-watchdog.org>
> >> Cc: Guenter Roeck <linux at roeck-us.net>
> >> Cc: Joel Stanley <joel at jms.id.au>
> >> Cc: Andrew Jeffery <andrew at codeconstruct.com.au>
> >> Cc: Eddie James <eajames at linux.ibm.com>
> >> ---
> >>   drivers/watchdog/aspeed_wdt.c | 7 +++++++
> >>   1 file changed, 7 insertions(+)
> >>
> >> diff --git a/drivers/watchdog/aspeed_wdt.c b/drivers/watchdog/aspeed_wdt.c
> >> index b4773a6aaf8c..520d8aba12a5 100644
> >> --- a/drivers/watchdog/aspeed_wdt.c
> >> +++ b/drivers/watchdog/aspeed_wdt.c
> >> @@ -187,6 +187,13 @@ static int aspeed_wdt_set_pretimeout(struct 
> >> watchdog_device *wdd,
> >>       u32 actual = pretimeout * WDT_RATE_1MHZ;
> >>       u32 s = wdt->cfg->irq_shift;
> >>       u32 m = wdt->cfg->irq_mask;
> >> +    u32 reload = readl(wdt->base + WDT_RELOAD_VALUE);
> >> +
> >
> > It is unusual to use a register value here and not the configured timeout
> > value. I would have assumed that pretimeout is compared against wdt->timout,
> > not against the register value, and that the multiplication with WDT_RATE_1MHZ
> > is done after validation. This needs an explanation.
> It was supposed to be a straight-forward way to check if the pretimeout value is
> supported by the hardware. I can change to wdt->timeout if it is better.
>
> Further, in the case of wdt->timeout > max_hw_heartbeat_ms, shall we restrict
> the pretimeout to be larger than wdt->timeout - max_hw_heartbeat_ms  / 2? For
> the watchdog_kworker works in max_hw_heartbeat_ms  / 2 interval, pretimeout
> event may be triggered unexpected when watchdog is not pinged in
> (max_hw_heartbeat_ms - (timeout - pretimeout)).
>
> >
> >> +    if (actual >= reload)
> >> +        return -EINVAL;
> >> +
> >
> > On top of that, you'll also need to explain why watchdog_pretimeout_invalid()
> > and with it the validation in watchdog_set_pretimeout() does not work for this
> > watchdog and why this extra validation is necessary.
> watchdog_pretimeout_invalid() will return false if wdt->timeout == 0, but we
> can't determine the hardware pretimeout value if timeout == 0 here.
> >
> > Guenter
> >
> >> +    /* watchdog timer is counting down */
> >> +    actual = reload - actual;
> >>         wdd->pretimeout = pretimeout;
> >>       wdt->ctrl &= ~m;