Re: [PATCH V2 1/3] watchdog: imgpdc: Allow timeout to be set in device-tree

[Guenter Roeck]

On 04/02/2015 07:16 PM, Andrew Bresticker wrote:
> Hi Guenter,
>
> On Thu, Apr 2, 2015 at 6:52 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > On 04/02/2015 09:46 AM, Andrew Bresticker wrote:
> > > On Wed, Apr 1, 2015 at 6:08 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > > > On 04/01/2015 03:22 PM, James Hogan wrote:
> > > > > Hi Andrew,
> > > > >
> > > > > On Wed, Apr 01, 2015 at 10:43:14AM -0700, Andrew Bresticker wrote:
> > > > > > Since the heartbeat is statically initialized to its default value,
> > > > > > watchdog_init_timeout() will never look in the device-tree for a
> > > > > > timeout-sec value.  Instead of statically initializing heartbeat,
> > > > > > fall back to the default timeout value if watchdog_init_timeout()
> > > > > > fails.
> > > > >
> > > > >
> > > > >
> > > > > Whoops. Sorry about that. I wasn't aware that a timeout-sec value was
> > > > > expected. It isn't mentioned in the DT binding documentation for this
> > > > > device :-(.
> > > > >
> > > > > > Signed-off-by: Andrew Bresticker <abrestic@xxxxxxxxxxxx>
> > > > > > Cc: Ezequiel Garcia <ezequiel.garcia@xxxxxxxxxx>
> > > > > > Cc: James Hogan <james.hogan@xxxxxxxxxx>
> > > > > > ---
> > > > > > New for v2.
> > > > > > ---
> > > > > >     drivers/watchdog/imgpdc_wdt.c | 6 +++---
> > > > > >     1 file changed, 3 insertions(+), 3 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/watchdog/imgpdc_wdt.c
> > > > > > b/drivers/watchdog/imgpdc_wdt.c
> > > > > > index 0deaa4f..89b2abc 100644
> > > > > > --- a/drivers/watchdog/imgpdc_wdt.c
> > > > > > +++ b/drivers/watchdog/imgpdc_wdt.c
> > > > > > @@ -42,7 +42,7 @@
> > > > > >     #define PDC_WDT_MIN_TIMEOUT           1
> > > > > >     #define PDC_WDT_DEF_TIMEOUT           64
> > > > > >
> > > > > > -static int heartbeat = PDC_WDT_DEF_TIMEOUT;
> > > > > > +static int heartbeat;
> > > > > >     module_param(heartbeat, int, 0);
> > > > > >     MODULE_PARM_DESC(heartbeat, "Watchdog heartbeats in seconds "
> > > > > >           "(default=" __MODULE_STRING(PDC_WDT_DEF_TIMEOUT) ")");
> > > > > > @@ -195,9 +195,9 @@ static int pdc_wdt_probe(struct platform_device
> > > > > > *pdev)
> > > > > >
> > > > > >           ret = watchdog_init_timeout(&pdc_wdt->wdt_dev, heartbeat,
> > > > > > &pdev->dev);
> > > > > >           if (ret < 0) {
> > > > > > -               pdc_wdt->wdt_dev.timeout =
> > > > > > pdc_wdt->wdt_dev.max_timeout;
> > > > > > +               pdc_wdt->wdt_dev.timeout = PDC_WDT_DEF_TIMEOUT;
> > > > >
> > > > >
> > > > >
> > > > > The watchdog_init_timeout kerneldoc comment suggests that the old value
> > > > > should be the default timeout, i.e. that timeout should be set to
> > > > > PDC_WDT_DEF_TIMEOUT before calling watchdog_init_timeout, rather than
> > > > > whenever ret < 0.
> > > > >
> > > > > Indeed, if heartbeat is set to an invalid non-zero value,
> > > > > watchdog_init_timeout will still try and set timeout from DT, but also
> > > > > still returns -EINVAL regardless of whether that succeeds, and this
> > > > > would incorrectly override the timeout from DT with the hardcoded
> > > > > default.
> > > > >
> > > > > >                   dev_warn(&pdev->dev,
> > > > > > -                        "Initial timeout out of range! setting max
> > > > > > timeout\n");
> > > > > > +                        "Initial timeout out of range! setting default
> > > > > > timeout\n");
> > > > >
> > > > >
> > > > >
> > > > > It feels wrong for a presumably safe & normal situation (i.e. no default
> > > > > in DT, which arguably shouldn't contain policy anyway) to show a
> > > > > warning, but it can also show due to an invalid module parameter (or
> > > > > invalid DT property) which is most definitely justified.
> > > >
> > > > Agreed. I would suggest to leave that part alone and set the default
> > > > prior
> > > > to calling watchdog_init_timeout().
> > >
> > >
> > > Yes, but I think James' concern here was that we'd now get a
> > > dev_warn() in the normal case where no timeout is specified via module
> > > parameter or DT.
> > My understanding is that watchdog_init_timeout only returns an error if
> > the second parameter is not 0 and invalid, or if the timeout-sec property
> > has been provided and is invalid. I am not entirely sure I understand
> > why you think this is a problem. Can you please explain ?
>
> Unless I've gone completely insane, I'm pretty sure this will return
> -EINVAL if timeout_parm is 0 and timeout-sec is not present:
>
> int watchdog_init_timeout(struct watchdog_device *wdd,
>                                  unsigned int timeout_parm, struct device *dev)
> {
>          unsigned int t = 0;
>          int ret = 0;
>
>          watchdog_check_min_max_timeout(wdd);
>
>          /* try to get the timeout module parameter first */
>          if (!watchdog_timeout_invalid(wdd, timeout_parm) && timeout_parm) {
>                  wdd->timeout = timeout_parm;
>                  return ret;
>          }
>          if (timeout_parm)
>                  ret = -EINVAL;
>
>          /* try to get the timeout_sec property */
>          if (dev == NULL || dev->of_node == NULL)
>                  return ret;
>          of_property_read_u32(dev->of_node, "timeout-sec", &t);
>          if (!watchdog_timeout_invalid(wdd, t) && t)
>                  wdd->timeout = t;
>          else
>                  ret = -EINVAL;
>
>          return ret;
> }
>
> That said, the behavior you describe makes more sense, so perhaps
> watchdog_init_timeout() should be updated to match.

Ah yes, you are right, that last else case. Guess we'll need input from Wim
on how to handle this.

Guenter

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