[linux-dvb] Re: Another issue: frontend timeout value and low symbol rates

[Johannes Stezenbach <js@convergence.de>]

Andrew de Quincey wrote:
> 
> > Well, the DVB API as specified by Nokia says that FE_SET_FRONTEND
> > should start tuning, and the result (failure or success) is relayed
> > to the application by means of an event with FE_GET_EVENT.
> > I.e. one FE_SET_FRONTEND -> one FE_GET_EVENT. But it's also
> > possible for the frontend to generate additional events, e.g.
> > when the cable is unplugged and replugged.
> >
> > The frontend code should do what it can get a lock, and if that
> > fails, report the failure. IMHO this is the job of the driver,
> > because the timeouts depend on the type of frontend (or even
> > on the frontend making and model).
> >
> > But Holger thought differently, and said the application should
> > do its own timeouts, because the driver cannot know how
> > long it wants to wait before assuming failure. The code
> > also generated superflous events during tuning. After some
> > debate he put in the current FE_TIMEDOUT cruft (with an arbitrarily
> > chosen timeout), which essentially means "your tuning attempt
> > already timed out, so the following tuning-failed event is
> > superflous and can be discarded". Or something like this
> > (I never quite understood it).
> 
> Yeah, that is pretty much my thinking. I don't see how the Nokia API could 
> actually work in the real world. Unless we were prepared to break with the 
> Nokia API, and have apps do timeouts, I don't know if theres any point in me 
> attempting to fix it, because whatever I do, it will be a hack, and not work 
> in all situations. The driver just doesn't have enough information on what 
> the app is wanting it to do.
> 
> If there _isn't_ a problem with breaking the Nokia API, I would be glad to 
> have a look. 
> 
> If there is, all I have to do to fix my stuff is ignore the FE_TIMEDOUT bit.

Maybe my description was unclear: FE_TIMEDOUT is Holger's invention.

The Nokia API just says "tuning is asynchronous", i.e. started by
FE_SET_FRONTEND, and finished when the driver has a signal or gives up.
(-> FE event). IMHO the event makes sense, FE_TIMEDOUT not.

Johannes


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