[linux-dvb] [PATCH] Add missing S2 caps flag to S2API

Klaus Schmidinger Klaus.Schmidinger at cadsoft.de
Mon Nov 24 10:06:35 CET 2008


On 24.11.2008 08:12, Artem Makhutov wrote:
> Hello,
> 
> Klaus Schmidinger schrieb:
>> The attached patch adds a capability flag that allows an application
>> to determine whether a particular device can handle "second generation
>> modulation" transponders. This is necessary in order for applications
>> to be able to decide which device to use for a given channel in
>> a multi device environment, where DVB-S and DVB-S2 devices are mixed.
>>
>> It is assumed that a device capable of handling "second generation
>> modulation" can implicitly handle "first generation modulation".
>> The flag is not named anything with DVBS2 in order to allow its
>> use with future DVBT2 devices as well (should they ever come).
>>
>> Signed-off by: Klaus Schmidinger <Klaus.Schmidinger at cadsoft.de>
> 
> Wouldn't it be better to add something like this:
> 
> FE_CAN_8PSK
> FE_CAN_16APSK
> FE_CAN_32APSK
> 
> or
> 
> FE_CAN_DVBS2
> 
> Instead of FE_CAN_2ND_GEN_MODULATION ? It is too generic for me.

Well, it's bad enough that we have to "guess" which kind of
delivery system it is by looking at feinfo.type. If it's FE_QPSK
then it's DVB-S (or DVB-S2), if it's FE_OFDM then it's DVB-T etc.,
etc. The "multiproto" API had this cleaned up and introduced a
clean way of finding out the delivery systems(!) a particular device
can handle. Unfortunately, as we all know, this approach has been
dismissed.

Using some additional flags for "guessing" whether it's DVB-S2
doesn't seem like a clean solution to me. Why not simply state
the obvious? After all, the DVB standard for DVB-S2 speaks of
"second generation modulation", that's why I named this flag
that way. And since S2API can only handle a single delivery system
at a time (as opposed to multiproto, where the delivery systems
were flags, so a device could support several of them), it
somehow made sense to me to have a flag that could later also
be used for "second generation DVB-T" devices.

But I don't want to start another political fight here. All I need
is a way to determine whether or not a device supports DVB-S2.
If the commonly agreed on way to do this is to guess it by
looking at FE_CAN_xyPSK capability flags, so be it. However, so
far none of the "experts" cared about answering my initial
question "How to determine DVB-S2 capability in S2API?", so
I guessed the only way to get something to work was doing something
about it ;-)

Klaus



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