[media] dib7000p: Callibrate signal strength

Calibrate the signal strength to dB.

For this callibration, I used adapter 0 (antenna 1), connected
via a normal cable to a DTF-2111 generator.

The same cabling and RF generator connected to adapter 1
(antenna 2) has a difference of +3dBm (signal was stronger
there).

Yet, changing the RF for a difference of, let's say, 6dB
reflected on a 6dB difference at the measured signal, with
is good.

So, the signal strengh can indeed be used to measure the
antenna gain, if the antenna is repositioned. It is
not precise to measure the absolute dBm value, however.
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/dvb-frontends/dib7000p.c

@@ -1693,13 +1693,56 @@ struct linear_segments {
  * This table should be empirically determinated by measuring the signal
  * strength generated by a RF generator directly connected into
  * a device.
+ * This table was determinated by measuring the signal strength generated
+ * by a DTA-2111 RF generator directly connected into a dib7000p device
+ * (a Hauppauge Nova-TD stick), using a good quality 3 meters length
+ * RC6 cable and good RC6 connectors, connected directly to antenna 1.
+ * As the minimum output power of DTA-2111 is -31dBm, a 16 dBm attenuator
+ * were used, for the lower power values.
+ * The real value can actually be on other devices, or even at the
+ * second antena input, 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 to adjust antennas.
  */
-/* FIXME: Calibrate the table */
-
-#define DB_OFFSET 0
+#define DB_OFFSET 131000
 
 static struct linear_segments strength_to_db_table[] = {
-	{ 65535,  65535},
+	{ 63630, DB_OFFSET - 20500},
+	{ 62273, DB_OFFSET - 21000},
+	{ 60162, DB_OFFSET - 22000},
+	{ 58730, DB_OFFSET - 23000},
+	{ 58294, DB_OFFSET - 24000},
+	{ 57778, DB_OFFSET - 25000},
+	{ 57320, DB_OFFSET - 26000},
+	{ 56779, DB_OFFSET - 27000},
+	{ 56293, DB_OFFSET - 28000},
+	{ 55724, DB_OFFSET - 29000},
+	{ 55145, DB_OFFSET - 30000},
+	{ 54680, DB_OFFSET - 31000},
+	{ 54293, DB_OFFSET - 32000},
+	{ 53813, DB_OFFSET - 33000},
+	{ 53427, DB_OFFSET - 34000},
+	{ 52981, DB_OFFSET - 35000},
+
+	{ 52636, DB_OFFSET - 36000},
+	{ 52014, DB_OFFSET - 37000},
+	{ 51674, DB_OFFSET - 38000},
+	{ 50692, DB_OFFSET - 39000},
+	{ 49824, DB_OFFSET - 40000},
+	{ 49052, DB_OFFSET - 41000},
+	{ 48436, DB_OFFSET - 42000},
+	{ 47836, DB_OFFSET - 43000},
+	{ 47368, DB_OFFSET - 44000},
+	{ 46468, DB_OFFSET - 45000},
+	{ 45597, DB_OFFSET - 46000},
+	{ 44586, DB_OFFSET - 47000},
+	{ 43667, DB_OFFSET - 48000},
+	{ 42673, DB_OFFSET - 49000},
+	{ 41816, DB_OFFSET - 50000},
+	{ 40876, DB_OFFSET - 51000},
 	{     0,      0},
 };
 
@@ -1853,9 +1896,6 @@ static int dib7000p_get_stats(struct dvb_frontend *demod, fe_status_t stat)
 			       ARRAY_SIZE(strength_to_db_table)) - DB_OFFSET;
 	c->strength.stat[0].svalue = db;
 
-	/* FIXME: Remove this when calibrated to DB */
-	c->strength.stat[0].scale = FE_SCALE_COUNTER;
-
 	/* UCB/BER/CNR measures require lock */
 	if (!(stat & FE_HAS_LOCK)) {
 		c->cnr.len = 1;