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[media] dvb_core: estimate bw for all non-terrestial systems 

Instead of just estimating the bandwidth for DVB-C annex A/C,
also fill it at the core for ATSC and DVB-C annex B. This
simplifies the logic inside the tuners, as all non-satellite
tuners can just use c->bandwidth_hz for all supported
delivery systems.

It could make sense to latter use it also for satellite
systems, as several DVB-S drivers have their own calculus.
However, on DVB-S2 the bw estimation is a little more complex,
and the existing drivers have some optimized calculus for
bandwidth. So, let's not touch on it for now.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Mauro Carvalho Chehab 2011-12-21 08:27:20 -03:00
parent 0349471bc5
commit 0607d07780
1 changed files with 27 additions and 8 deletions
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35
drivers/media/dvb/dvb-core/dvb_frontend.c
View File

@ -1180,19 +1180,38 @@ static void dtv_property_adv_params_sync(struct dvb_frontend *fe)
}
/*
* On DVB-C, the bandwidth is a function of roll-off and symbol rate.
* The bandwidth is required for DVB-C tuners, in order to avoid
* inter-channel noise. Instead of estimating the minimal required
* bandwidth on every single driver, calculates it here and fills
* it at the cache bandwidth parameter.
* Be sure that the bandwidth will be filled for all
* non-satellite systems, as tuners need to know what
* low pass/Nyquist half filter should be applied, in
* order to avoid inter-channel noise.
*
* ISDB-T and DVB-T/T2 already sets bandwidth.
* ATSC and DVB-C don't set, so, the core should fill it.
*
* On DVB-C Annex A and C, the bandwidth is a function of
* the roll-off and symbol rate. Annex B defines different
* roll-off factors depending on the modulation. Fortunately,
* Annex B is only used with 6MHz, so there's no need to
* calculate it.
*
* While not officially supported, a side effect of handling it at
* the cache level is that a program could retrieve the bandwidth
* via DTV_BANDWIDTH_HZ, wich may be useful for test programs.
* via DTV_BANDWIDTH_HZ, which may be useful for test programs.
*/
if (c->delivery_system == SYS_DVBC_ANNEX_A)
switch (c->delivery_system) {
case SYS_ATSC:
case SYS_DVBC_ANNEX_B:
c->bandwidth_hz = 6000000;
break;
case SYS_DVBC_ANNEX_A:
rolloff = 115;
if (c->delivery_system == SYS_DVBC_ANNEX_C)
break;
case SYS_DVBC_ANNEX_C:
rolloff = 113;
break;
default:
break;
}
if (rolloff)
c->bandwidth_hz = (c->symbol_rate * rolloff) / 100;
}