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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: Jean Delvare <khali@linux-fr.org>
Cc: Steven Toth <stoth@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Jean Delvare 2012-02-12 15:03:03 -03:00 committed by Mauro Carvalho Chehab
parent 6c5637e4ed
commit 06302ffbb4
1 changed files with 19 additions and 3 deletions
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22
drivers/media/dvb/frontends/cx22702.c
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@ -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;
}