[media] stb0899: fix the limits for signal strength values

stb0899: fix the limits for signal strength values

stb0899_read_signal_strength() adds an offset to the result of the table lookup.
That offset must correspond to the lowest value in the lookup table, to make sure
the result doesn't get below 0, which would mean a "very high" value since the
parameter is unsigned.
'strength' and 'snr' need to be initialized to 0 to make sure they have a
defined result in case there is no "internal->lock".
Signed-off-by: NKlaus Schmidinger <Klaus.Schmidinger@tvdr.de>
Cc: Manu Abraham <abraham.manu@gmail.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/dvb/frontends/stb0899_drv.c

@@ -67,7 +67,7 @@ static const struct stb0899_tab stb0899_cn_tab[] = {
  * Crude linear extrapolation below -84.8dBm and above -8.0dBm.
  */
 static const struct stb0899_tab stb0899_dvbsrf_tab[] = {
-	{ -950,	-128 },
+	{ -750,	-128 },
 	{ -748,	 -94 },
 	{ -745,	 -92 },
 	{ -735,	 -90 },
@@ -131,7 +131,7 @@ static const struct stb0899_tab stb0899_dvbs2rf_tab[] = {
 	{ -730,	13645 },
 	{ -750,	13909 },
 	{ -766,	14153 },
-	{ -999,	16383 }
+	{ -950,	16383 }
 };
 
 /* DVB-S2 Es/N0 quant in dB/100 vs read value * 100*/
@@ -964,6 +964,7 @@ static int stb0899_read_signal_strength(struct dvb_frontend *fe, u16 *strength)
 
 	int val;
 	u32 reg;
+	*strength = 0;
 	switch (state->delsys) {
 	case SYS_DVBS:
 	case SYS_DSS:
@@ -987,7 +988,7 @@ static int stb0899_read_signal_strength(struct dvb_frontend *fe, u16 *strength)
 			val = STB0899_GETFIELD(IF_AGC_GAIN, reg);
 
 			*strength = stb0899_table_lookup(stb0899_dvbs2rf_tab, ARRAY_SIZE(stb0899_dvbs2rf_tab) - 1, val);
-			*strength += 750;
+			*strength += 950;
 			dprintk(state->verbose, FE_DEBUG, 1, "IF_AGC_GAIN = 0x%04x, C = %d * 0.1 dBm",
 				val & 0x3fff, *strength);
 		}
@@ -1009,6 +1010,7 @@ static int stb0899_read_snr(struct dvb_frontend *fe, u16 *snr)
 	u8 buf[2];
 	u32 reg;
 
+	*snr = 0;
 	reg  = stb0899_read_reg(state, STB0899_VSTATUS);
 	switch (state->delsys) {
 	case SYS_DVBS: