Re: [PATCH 1/2] watchdog: sbsa_wdog: Fix the timeout calculation while programming

[George Cherian]

> -----Original Message-----
> From: Guenter Roeck <groeck7@xxxxxxxxx> On Behalf Of Guenter Roeck
> Sent: Tuesday, February 7, 2023 9:34 PM
> To: George Cherian <gcherian@xxxxxxxxxxx>; wim@xxxxxxxxxxxxxxxxxx;
> zhangshaokun@xxxxxxxxxxxxx
> Cc: linux-watchdog@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH 1/2] watchdog: sbsa_wdog: Fix the timeout
> calculation while programming
> 
> 
> ----------------------------------------------------------------------
> On 2/6/23 20:46, George Cherian wrote:
> > The time out calculation done in sbsa_gwdt_set_timeout() would always
> > return a 32-bit value. Use proper typecasting to make sure the overflow
> > values are captured.
> >
> > Fixes: abd3ac7902fb ("watchdog: sbsa: Support architecture version 1")
> >
> > Signed-off-by: George Cherian <george.cherian@xxxxxxxxxxx>
> > ---
> >   drivers/watchdog/sbsa_gwdt.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/watchdog/sbsa_gwdt.c
> b/drivers/watchdog/sbsa_gwdt.c
> > index 9791c74aebd4..aaa3f5631f29 100644
> > --- a/drivers/watchdog/sbsa_gwdt.c
> > +++ b/drivers/watchdog/sbsa_gwdt.c
> > @@ -152,14 +152,14 @@ static int sbsa_gwdt_set_timeout(struct
> watchdog_device *wdd,
> >   	wdd->timeout = timeout;
> >
> >   	if (action)
> > -		sbsa_gwdt_reg_write(gwdt->clk * timeout, gwdt);
> > +		sbsa_gwdt_reg_write((u64)gwdt->clk * (u64)timeout, gwdt);
> >   	else
> >   		/*
> >   		 * In the single stage mode, The first signal (WS0) is ignored,
> >   		 * the timeout is (WOR * 2), so the WOR should be
> configured
> >   		 * to half value of timeout.
> >   		 */
> > -		sbsa_gwdt_reg_write(gwdt->clk / 2 * timeout, gwdt);
> > +		sbsa_gwdt_reg_write((u64)gwdt->clk / 2 * (u64)timeout,
> gwdt);
> >
> >   	return 0;
> >   }
> 
> The driver sets max_hw_heartbeat_ms. It is its responsibility to clamp
> the timeout value written into the controller to the configured limit
> to avoid confusing the watchdog core. Something like
> 
> 	timeout = clamp(timeout, 0, wdd->max_hw_heartbeat_ms / 1000);
> 
> This also solves the problem in patch 2 since it guarantees that the
> resulting register value is <= U32_MAX for version 0.

 Thanks for the review.  I will update accordingly and post a v2.

> 
> Guenter

Regards,
-George