[PATCH v2 3/4] media: tda8290: report FM signal strength on the TDA8295

[Ext745 <stealth3m@yahoo.com>]

In FM radio mode the TDA8295's picture carrier PLL is off, so the H-PLL
lock bit that tda8295_has_signal() reads is never set and radio always
reports 0 % signal. In radio mode use the tuner IF AGC level instead
(0x28, T_IF_AGC_STAT): 0xff is maximum gain (no signal), strong local
stations read around 0x90.

Tested on an HVR-1950 in a dense urban FM band (stations 400 kHz
apart): 30 to 84 % on local stations, 0 to 26 % where the band is empty
(87.9-88.9 MHz); TV unchanged.  The AGC acts on the whole IF passband,
so between closely spaced stations the meter stays near their level
(73 to 86 % across 100-104 MHz): it shows that a signal is there, not
that this exact channel holds a station.  Seek in such a band can't rely
on the level alone.

Assisted-by: Claude Opus 5.5
Signed-off-by: Ext745 <stealth3m@yahoo.com>
---
v2:
- return -EREMOTEIO if the IF AGC read fails

 drivers/media/tuners/tda8290.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/media/tuners/tda8290.c b/drivers/media/tuners/tda8290.c
index 9ff0aa8cb..7441a5872 100644
--- a/drivers/media/tuners/tda8290.c
+++ b/drivers/media/tuners/tda8290.c
@@ -384,8 +384,23 @@ static int tda8295_has_signal(struct dvb_frontend *fe, u16 *signal)
 	struct tda8290_priv *priv = fe->analog_demod_priv;
 
 	unsigned char hvpll_stat = 0x26;
+	unsigned char t_if_agc_stat = 0x28;
 	unsigned char ret;
 
+	if (priv->tda8290_easy_mode == 0x80) {
+		/*
+		 * FM radio: the picture carrier PLL is off, so the H-PLL
+		 * lock bit is never set.  Use the tuner IF AGC level
+		 * instead: 0xff is maximum gain (no signal), strong local
+		 * stations read around 0x90.
+		 */
+		if (tuner_i2c_xfer_send_recv(&priv->i2c_props,
+					     &t_if_agc_stat, 1, &ret, 1) != 1)
+			return -EREMOTEIO;
+		*signal = min(0xff - ret, 0x80) * 65535 / 0x80;
+		return 0;
+	}
+
 	tuner_i2c_xfer_send_recv(&priv->i2c_props, &hvpll_stat, 1, &ret, 1);
 	*signal = (ret & 0x01) ? 65535 : 0;
 	return 0;
-- 
2.53.0