[linux-dvb] Asys P7131 Hybrid: DVB out of range

Trent Piepho xyzzy at speakeasy.org
Thu Sep 6 17:47:49 CEST 2007

On Thu, 6 Sep 2007, Mauro Carvalho Chehab wrote:
> > > The limits are comming from the tda10046 info.  I think the correct thing
> > > to do here is to not have the tda1004x driver define frequency limits, as
> > > it's the tuner that has the limits.
> >
> > Nak. You must not remove these limits unless you make sure
> > that all tuner drivers which might be attached to this demod
> > have non-zero frequency limits.

So the incorrect limits should be left there?  That isn't right either.

> IMO, the better would be not to initialize frequency ranges at the
> demods (since this is tuner stuff).

At least for many demods, the frequency range supported is determined by
the tuner.  One could have a chip that combines the demod and tuner
functions, or a system where the demod is somehow involved in tuning and
has some limit.  But that is not the case here.

> If you are afraid of having a tuner driver with improper values, add a
> check can be added, at dvb frontend core, to use the maximum allowed
> frequency range, if frequency_max is not defined. The better, however,
> is to fix the tuner drivers without frequency limits.

This would be easy to do.  There is already a function,
dvb_frontend_get_frequeny_limits(), that does this.  It prints a warning
message if neither the demod nor the tuner define a limit.  In this case,
it returns zero for the max frequency, so any attempt to tune with a driver
broken like this will fail.  It could easily return ULONG_MAX in this case,
so tuning would work but there would still be the warning message.

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