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

[Andrew Jeffery <andrew@codeconstruct.com.au>]

On Mon, 2025-02-17 at 21:33 -0800, 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@linux.alibaba.com>
> > 
> > Cc: Wim Van Sebroeck <wim@linux-watchdog.org>
> > Cc: Guenter Roeck <linux@roeck-us.net>
> > Cc: Joel Stanley <joel@jms.id.au>
> > Cc: Andrew Jeffery <andrew@codeconstruct.com.au>
> > Cc: Eddie James <eajames@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.

+1

> 
> > +       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.

+1 as well.

Further, the logic looks broken regardless for the AST2400 where
there's no pretimeout support. aspeed_wdt_set_pretimeout() should error
out if wdt->cfg->irq_mask is 0.

Andrew