Re: [PATCH 4/8] watchdog: Make set_timeout function optional

[Guenter Roeck]

Hi Uwe,

On 08/04/2015 08:38 AM, Uwe Kleine-König wrote:
> Hello,
>
> On Mon, Aug 03, 2015 at 07:13:30PM -0700, Guenter Roeck wrote:
> > For some watchdogs, the hardware timeout is fixed, and the
> > watchdog driver depends on the watchdog core to handle the
> > actual timeout. In this situation, the watchdog driver might
> > only set the 'timeout' variable but do nothing else.
> > This can as well be handled by the infrastructure, so make
> > the set_timeout callback optional. If WDIOF_SETTIMEOUT is
> > configured but the .set_timeout callback is not available,
> > update the timeout variable in the infrastructure code.
> >
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> >   Documentation/watchdog/watchdog-kernel-api.txt | 4 ++++
> >   drivers/watchdog/watchdog_dev.c                | 9 ++++++---
> >   2 files changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/watchdog/watchdog-kernel-api.txt b/Documentation/watchdog/watchdog-kernel-api.txt
> > index 7fda3c86cf46..2f1a4ad7e565 100644
> > --- a/Documentation/watchdog/watchdog-kernel-api.txt
> > +++ b/Documentation/watchdog/watchdog-kernel-api.txt
> > @@ -178,6 +178,10 @@ they are supported. These optional routines/operations are:
> >     because the watchdog does not necessarily has a 1 second resolution).
> >     (Note: the WDIOF_SETTIMEOUT needs to be set in the options field of the
> >     watchdog's info structure).
> > +  If the watchdog driver does not have to perform any action but setting the
> > +  timeout value of the watchdog_device, this callback can be omitted.
> > +  If set_timeout is not provided but WDIOF_SETTIMEOUT is set, the watchdog
> > +  infrastructure updates the timeout value of the watchdog_device internally.
> What is the semantic of struct watchdog_device.timeout? Is it the
> corrently configured hw-timeout? Or what userspace sees? In the former
> case timeout shouldn't be updated. And in the latter case it's wrong
> that the worker thread uses this member to determine the needed rate for
> it's auto pinging.

.timeout is what user-space sees, but it is also what may be configured
into the hardware, depending on the value of max_hw_timeout and on the driver.

For example, if timeout = 5s and max_hw_timeout = 6000ms, the driver would (or might)
configure the _current_ hardware timeout to 5s. The worker would not be activated.
If, on the other side, timeout = 10s and max_hw_timeout = 6000ms, the driver would
configure the hardware timeout to 6s, the worker would send a heartbeat every
3 seconds, and user space would be expected to send a heartbeat every 5 seconds
or so (assuming it uses timeout/2 to determine when to send heartbeats).

Thanks,
Guenter

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