V4L/DVB (6501): stv0297: Signal strength fixes

Fixes the signal strength value (higher value = higher signal strength)
and scales the value to the range of 0..ffff. The characteristic itself
is wrong. To get proper values on a TT-C2300 in the range of 40..60%
real signal strength, the values from the patch should be divide by two.
The attached patch doesn't fix the characteristic.

Signed-off-by: Hartmut Birr <e9hack@googlemail.com>
Signed-off-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/dvb/frontends/stv0297.c

@@ -358,11 +358,23 @@ static int stv0297_read_ber(struct dvb_frontend *fe, u32 * ber)
 static int stv0297_read_signal_strength(struct dvb_frontend *fe, u16 * strength)
 {
 	struct stv0297_state *state = fe->demodulator_priv;
-	u8 STRENGTH[2];
-
-	stv0297_readregs(state, 0x41, STRENGTH, 2);
-	*strength = (STRENGTH[1] & 0x03) << 8 | STRENGTH[0];
-
+	u8 STRENGTH[3];
+	u16 tmp;
+
+	stv0297_readregs(state, 0x41, STRENGTH, 3);
+	tmp = (STRENGTH[1] & 0x03) << 8 | STRENGTH[0];
+	if (STRENGTH[2] & 0x20) {
+		if (tmp < 0x200)
+			tmp = 0;
+		else
+			tmp = tmp - 0x200;
+	} else {
+		if (tmp > 0x1ff)
+			tmp = 0;
+		else
+			tmp = 0x1ff - tmp;
+	}
+	*strength = (tmp << 7) | (tmp >> 2);
 	return 0;
 }