diff options
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/media/dvb/dvb-core/dvb_frontend.c | 35 |
1 files changed, 27 insertions, 8 deletions
diff --git a/drivers/media/dvb/dvb-core/dvb_frontend.c b/drivers/media/dvb/dvb-core/dvb_frontend.c index 2e4bddec9b32..7ea79dffa970 100644 --- a/drivers/media/dvb/dvb-core/dvb_frontend.c +++ b/drivers/media/dvb/dvb-core/dvb_frontend.c @@ -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; } |