[linux-dvb] Re: [RFC][ANNOUNCE] blindscan: auto search everything

[Johannes Stezenbach <js@convergence.de>]

Roberto Ragusa wrote:
> Holger Waechtler <holger@qanu.de> wrote:
> 
> > struct dvb_fe_scan_spec {
> > 	unsigned freq_start;
> > 	unsigned freq_end;
> > 	unsigned srate_start;
> > 	unsigned srate_end;
> > }
> > 
> > A similiar approach works for the mt352 DVB-T demod, there the srate 
> > fields are not required but bandwidth and the scan_weak_channels bit 
> > have to be configured. What do you think?
> 
> The auto symbol rate capability is not exactly a scan.
> Between a start frequency and an end frequency you can find many signals.
> But in a sr range you can only find one signal.
> 
> So, the idea of suspending and resuming is not applicable.
> Having freq and sr together in a struct doesn't look right, as freq
> is tipically fixed.
> 
> After rereading what you wrote... are you saying that the core of the
> blindscan program should be moved into the kernel?

IIRC Holger told me that the mt3?2 frontends can do the whole scan
automatically? Doing it in the kernel sounds wrong.


> So the problem is reduced to:
> - how do we specify a start and end sr?
> We have one 32 bit field in the tuning struct.
> We can introduce a struct with 2 32 bit fields, but how do we
> link it to the tuning struct?
> Is it reasonable to extend the dvb_qpsk_parameters?

We cannot break binary compatibilty for the existing tuning API.

> We could add a symbol_rate_uncertainty and specify center and width
> of the interval instead of start end, but that wouldn't be a real
> parameter (in fact there is nothing reasonable to return
> on FE_GET_FRONTEND).
> 
> We want to fit two 32 bit values into a 32 bit space, that's
> the core of the problem, IMHO.
> 
> The best I can think is
>   bit 31-30 00: normal sr, 01: interval, 10:rsvd, 11:rsvd
>   bit 29-15 15 bit, start sr
>   bit 14-0  15 bit, end sr

We can always add new ioctls. To me it doesn't feel right
to cram the scan functionality into the normal FE_SET_FRONTEND ioctl.

Johannes