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authorMauro Carvalho Chehab <mchehab@redhat.com>2011-07-28 22:49:43 +0400
committerMauro Carvalho Chehab <mchehab@redhat.com>2011-07-29 00:09:46 +0400
commitcf845297d592339bcf0839298c4319633df3173a (patch)
treee845f7163fbbd20f61600c334e3fd7ed539bce30 /drivers/media
parent86cf786c04541c18febc897686a0d5bea29ce688 (diff)
downloadlinux-cf845297d592339bcf0839298c4319633df3173a.tar.xz
[media] tda18271c2dd: Fix saw filter configuration for DVB-C @6MHz
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>
Diffstat (limited to 'drivers/media')
-rw-r--r--drivers/media/dvb/frontends/tda18271c2dd.c20
1 files changed, 19 insertions, 1 deletions
diff --git a/drivers/media/dvb/frontends/tda18271c2dd.c b/drivers/media/dvb/frontends/tda18271c2dd.c
index 2eb3a31a715c..0384e8da4f5e 100644
--- a/drivers/media/dvb/frontends/tda18271c2dd.c
+++ b/drivers/media/dvb/frontends/tda18271c2dd.c
@@ -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 {