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Commit 06302ffb authored by Jean Delvare's avatar Jean Delvare Committed by Mauro Carvalho Chehab
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[media] cx22702: Fix signal strength 



The signal strength value returned is not quite correct, it decreases
when I increase the gain of my antenna, and vice versa. It also
doesn't span over the whole 0x0000-0xffff range. Compute a value which
at least increases when signal strength increases, and spans the whole
allowed range.

In practice I get 67% with my antenna fully amplified and 51% with
no amplification. This is close enough to what I get on my other
DVB-T adapter with the same antenna.

Signed-off-by: default avatarJean Delvare <khali@linux-fr.org>
Cc: Steven Toth <stoth@kernellabs.com>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@redhat.com>
parent 6c5637e4

drivers/media/dvb/frontends/cx22702.c

+19 −3
Original line number Diff line number Diff line
@@ -502,10 +502,26 @@ static int cx22702_read_signal_strength(struct dvb_frontend *fe, 
	u16 *signal_strength)

{

	struct cx22702_state *state = fe->demodulator_priv;

	u8 reg23;



	u16 rs_ber;

	rs_ber = cx22702_readreg(state, 0x23);

	*signal_strength = (rs_ber << 8) | rs_ber;

	/*

	 * Experience suggests that the strength signal register works as

	 * follows:

	 * - In the absence of signal, value is 0xff.

	 * - In the presence of a weak signal, bit 7 is set, not sure what

	 *   the lower 7 bits mean.

	 * - In the presence of a strong signal, the register holds a 7-bit

	 *   value (bit 7 is cleared), with greater values standing for

	 *   weaker signals.

	 */

	reg23 = cx22702_readreg(state, 0x23);

	if (reg23 & 0x80) {

		*signal_strength = 0;

	} else {

		reg23 = ~reg23 & 0x7f;

		/* Scale to 16 bit */

		*signal_strength = (reg23 << 9) | (reg23 << 2) | (reg23 >> 5);

	}



	return 0;

}