diff options
Diffstat (limited to 'drivers/media/dvb-frontends/dib8000.c')
| -rw-r--r-- | drivers/media/dvb-frontends/dib8000.c | 111 |
1 files changed, 92 insertions, 19 deletions
diff --git a/drivers/media/dvb-frontends/dib8000.c b/drivers/media/dvb-frontends/dib8000.c index faf469d1d437..7b10b73befbe 100644 --- a/drivers/media/dvb-frontends/dib8000.c +++ b/drivers/media/dvb-frontends/dib8000.c @@ -3843,35 +3843,108 @@ static const struct per_layer_regs per_layer_regs[] = { { 556, 581, 583 }, }; +struct linear_segments { + unsigned x; + signed y; +}; + +/* + * Table to estimate signal strength in dBm. + * This table was empirically determinated by measuring the signal + * strength generated by a DTA-2111 RF generator directly connected into + * a dib8076 device (a PixelView PV-D231U stick), using a good quality + * 3 meters RC6 cable and good RC6 connectors. + * The real value can actually be different on other devices, depending + * on several factors, like if LNA is enabled or not, if diversity is + * enabled, type of connectors, etc. + * Yet, it is better to use this measure in dB than a random non-linear + * percentage value, especially for antenna adjustments. + * On my tests, the precision of the measure using this table is about + * 0.5 dB, with sounds reasonable enough. + */ +static struct linear_segments strength_to_db_table[] = { + { 55953, 108500 }, /* -22.5 dBm */ + { 55394, 108000 }, + { 53834, 107000 }, + { 52863, 106000 }, + { 52239, 105000 }, + { 52012, 104000 }, + { 51803, 103000 }, + { 51566, 102000 }, + { 51356, 101000 }, + { 51112, 100000 }, + { 50869, 99000 }, + { 50600, 98000 }, + { 50363, 97000 }, + { 50117, 96000 }, /* -35 dBm */ + { 49889, 95000 }, + { 49680, 94000 }, + { 49493, 93000 }, + { 49302, 92000 }, + { 48929, 91000 }, + { 48416, 90000 }, + { 48035, 89000 }, + { 47593, 88000 }, + { 47282, 87000 }, + { 46953, 86000 }, + { 46698, 85000 }, + { 45617, 84000 }, + { 44773, 83000 }, + { 43845, 82000 }, + { 43020, 81000 }, + { 42010, 80000 }, /* -51 dBm */ + { 0, 0 }, +}; + +static u32 interpolate_value(u32 value, struct linear_segments *segments, + unsigned len) +{ + u64 tmp64; + u32 dx; + s32 dy; + int i, ret; + + if (value >= segments[0].x) + return segments[0].y; + if (value < segments[len-1].x) + return segments[len-1].y; + + for (i = 1; i < len - 1; i++) { + /* If value is identical, no need to interpolate */ + if (value == segments[i].x) + return segments[i].y; + if (value > segments[i].x) + break; + } + + /* Linear interpolation between the two (x,y) points */ + dy = segments[i - 1].y - segments[i].y; + dx = segments[i - 1].x - segments[i].x; + + tmp64 = value - segments[i].x; + tmp64 *= dy; + do_div(tmp64, dx); + ret = segments[i].y + tmp64; + + return ret; +} + static int dib8000_get_stats(struct dvb_frontend *fe, fe_status_t stat) { struct dib8000_state *state = fe->demodulator_priv; struct dtv_frontend_properties *c = &state->fe[0]->dtv_property_cache; int i, lock; - u64 tmp; u32 snr, val; + s32 db; u16 strength; /* Get Signal strength */ dib8000_read_signal_strength(fe, &strength); - - /* - * Estimate it in dBm - * This calculus was empirically determinated by measuring the signal - * strength generated by a DTA-2111 RF generator directly connected into - * a dib8076 device. The real value can actually be different on other - * devices, depending if LNA is enabled or not, if diversity is enabled, - * etc. - */ - if (strength == 65535) { - c->strength.stat[0].svalue = -22000; - } else { - tmp = strength * 25000L; - do_div(tmp, 11646); - c->strength.stat[0].svalue = tmp - 142569; - if (c->strength.stat[0].svalue > -22000) - c->strength.stat[0].svalue = -22000; - } + val = strength; + db = interpolate_value(val, + strength_to_db_table, + ARRAY_SIZE(strength_to_db_table)) - 131000; + c->strength.stat[0].svalue = db; /* Check if 1 second was elapsed */ if (!time_after(jiffies, state->get_stats_time)) |
