@@ -1123,6 +1123,21 @@ static int release(struct dvb_frontend *fe)
return 0;
}
+/*
+ * As defined on EN 300 429 Annex A and on ITU-T J.83 annex A, the DVB-C
+ * roll-off factor is 0.15.
+ * According with the specs, the amount of the needed bandwith is given by:
+ * Bw = Symbol_rate * (1 + 0.15)
+ * As such, the maximum symbol rate supported by 6 MHz is
+ * max_symbol_rate = 6 MHz / 1.15 = 5217391 Bauds
+ *NOTE: For ITU-T J.83 Annex C, the roll-off factor is 0.13. So:
+ * max_symbol_rate = 6 MHz / 1.13 = 5309735 Baud
+ * That means that an adjustment is needed for Japan,
+ * but, as currently DRX-K is hardcoded to Annex A, let's stick
+ * with 0.15 roll-off factor.
+ */
+#define MAX_SYMBOL_RATE_6MHz 5217391
+
static int set_params(struct dvb_frontend *fe,
struct dvb_frontend_parameters *params)
{
@@ -1146,7 +1161,10 @@ static int set_params(struct dvb_frontend *fe,
break;
}
else if (fe->ops.info.type == FE_QAM) {
- Standard = HF_DVBC_8MHZ;
+ if (params->u.qam.symbol_rate <= MAX_SYMBOL_RATE_6MHz)
+ Standard = HF_DVBC_6MHZ;
+ else
+ Standard = HF_DVBC_8MHZ;
} else
return -EINVAL;
do {
Currently, the driver assumes that all QAM carriers are spaced with 8MHz. This is wrong, and may decrease QoS on Countries like Brazil, that have DVB-C carriers with 6MHz-spaced. Fortunately, both ITU-T J-83 and EN 300 429 specifies a way to associate the symbol rate with the bandwidth needed for it. For ITU-T J-83 2007 annex A, the maximum symbol rate for 6 MHz is: 6 MHz / 1.15 = 5217391 Bauds For ITU-T J-83 2007 annex C, the maximum symbol rate for 6 MHz is: 6 MHz / 1.13 = 5309735 Bauds. As this tuner is currently used only for DRX-K, and it is currently hard-coded to annex A, I've opted to use the roll-off factor of 0.15, instead of 0.13. If we ever support annex C, the better would be to add a DVB S2API call to allow changing between Annex A and C, and add the 0.13 roll-off factor to it. This code is currently being used on other frontends, so I think we should later add a core function with this code, to warrant that it will be properly implemented everywhere. Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>