Re: SYS_DVBS vs. SYS_DVBS2

[Mauro Carvalho Chehab <mchehab+samsung@kernel.org>]

Em Wed, 19 Dec 2018 11:28:46 +0100
Josef Wolf <jw@raven.inka.de> escreveu:

> Hello experts,
> 
> hope I'm on the correct list for my question. Plese give me a pointer to the
> correct list if I'm off-topic here.
> 
> I would like to know how to know whether for a specific program SYS_DVBS or
> SYS_DVBS2 should be specified to the FE_SET_PROPERTY ioctl() call.

This is not specific to a program. It affects the hole transponder. Either
the transponder is DVB-S or DVB-S2.

> Is this somehow broadcasted in some PAT/PMT tables?

It is at the NAT tables. They contain all needed information to properly
tune into the transponders. There are different tables, depending if the
transponder is -S or -S2.

> Or is it possible to simple always specify SYS_DVBS2 and the kernel will
> manage the backwards compatibilities when a DVB-S transponder is specified in
> the tuning parameters?

The Kernel can't and shouldn't guess the tuning parameters. It depends
on userspace to parse the NAT tables and get it right.

If you use dvbv5-scan, for example, the logic at libdvbv5 will parse the
NAT tables for you and write the tuning parameters right for each
transponder, ensuring that every program inside that transponder will
receive the same tuning parameters.

Thanks,
Mauro