[media] xc4000: add support for signal strength measures

In xc4000 chipsets real signal and noise level is stored in register
0x0A and 0x0B,so we can use those registers to monitor signal strength.

I tested this patch on 2 different cards Leadtek DVR3200 and DTV2000H
Plus, both with same results, I used special antenna hubs (toner 4x, 6x,
8x and 12x) with mesured signal lost, both registers are in dB value,
first represent signal with limit value -113.5dB (should be -114dB) and
exactly match with test results. Second represents noise level also in
dB and there is no maximum value, but from tests we can drop everything
above 32dB which tuner realy can't use, signal was usable till 20dB
noise level.

In digital mode we can take signal strength but sadly noise level is not
relevant and real value is stored in demodulator for now just zl10353,
also digital mode is just for testing, because it needs changing other
parts of code which reads data only from demodulator.

In analog mode I was able to test only FM radio, signal level is not
important, it says something about cable and hub losts, but nothing
about real quality of reception, so even if we have signal level at
minimum 113dB we can still here radio, because of that it is displaied
only in debug mode, but for real signal level is used noise register
which is again very accurate, radio noise level was betwen 6-20dB for
good signal, 20-25dB for medium signal, and above 25dB signal is
unusable.

For now real benefit of this patch is only for FM radio mode.
Signed-off-by: Miroslav Slugen <thunder.mmm@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/common/tuners/xc4000.c

@@ -154,6 +154,8 @@ struct xc4000_priv {
 #define XREG_SNR          0x06
 #define XREG_VERSION      0x07
 #define XREG_PRODUCT_ID   0x08
+#define XREG_SIGNAL_LEVEL 0x0A
+#define XREG_NOISE_LEVEL  0x0B
 
 /*
    Basic firmware description. This will remain with
@@ -486,6 +488,16 @@ static int xc_get_quality(struct xc4000_priv *priv, u16 *quality)
 	return xc4000_readreg(priv, XREG_QUALITY, quality);
 }
 
+static int xc_get_signal_level(struct xc4000_priv *priv, u16 *signal)
+{
+	return xc4000_readreg(priv, XREG_SIGNAL_LEVEL, signal);
+}
+
+static int xc_get_noise_level(struct xc4000_priv *priv, u16 *noise)
+{
+	return xc4000_readreg(priv, XREG_NOISE_LEVEL, noise);
+}
+
 static u16 xc_wait_for_lock(struct xc4000_priv *priv)
 {
 	u16	lock_state = 0;
@@ -1089,6 +1101,8 @@ static void xc_debug_dump(struct xc4000_priv *priv)
 	u32	hsync_freq_hz = 0;
 	u16	frame_lines;
 	u16	quality;
+	u16	signal = 0;
+	u16	noise = 0;
 	u8	hw_majorversion = 0, hw_minorversion = 0;
 	u8	fw_majorversion = 0, fw_minorversion = 0;
 
@@ -1119,6 +1133,12 @@ static void xc_debug_dump(struct xc4000_priv *priv)
 
 	xc_get_quality(priv, &quality);
 	dprintk(1, "*** Quality (0:<8dB, 7:>56dB) = %d\n", quality);
+
+	xc_get_signal_level(priv, &signal);
+	dprintk(1, "*** Signal level = -%ddB (%d)\n", signal >> 8, signal);
+
+	xc_get_noise_level(priv, &noise);
+	dprintk(1, "*** Noise level = %ddB (%d)\n", noise >> 8, noise);
 }
 
 static int xc4000_set_params(struct dvb_frontend *fe)
@@ -1432,6 +1452,71 @@ static int xc4000_set_analog_params(struct dvb_frontend *fe,
 	return ret;
 }
 
+static int xc4000_get_signal(struct dvb_frontend *fe, u16 *strength)
+{
+	struct xc4000_priv *priv = fe->tuner_priv;
+	u16 value = 0;
+	int rc;
+
+	mutex_lock(&priv->lock);
+	rc = xc4000_readreg(priv, XREG_SIGNAL_LEVEL, &value);
+	mutex_unlock(&priv->lock);
+
+	if (rc < 0)
+		goto ret;
+
+	/* Informations from real testing of DVB-T and radio part,
+	   coeficient for one dB is 0xff.
+	 */
+	tuner_dbg("Signal strength: -%ddB (%05d)\n", value >> 8, value);
+
+	/* all known digital modes */
+	if ((priv->video_standard == XC4000_DTV6) ||
+	    (priv->video_standard == XC4000_DTV7) ||
+	    (priv->video_standard == XC4000_DTV7_8) ||
+	    (priv->video_standard == XC4000_DTV8))
+		goto digital;
+
+	/* Analog mode has NOISE LEVEL important, signal
+	   depends only on gain of antenna and amplifiers,
+	   but it doesn't tell anything about real quality
+	   of reception.
+	 */
+	mutex_lock(&priv->lock);
+	rc = xc4000_readreg(priv, XREG_NOISE_LEVEL, &value);
+	mutex_unlock(&priv->lock);
+
+	tuner_dbg("Noise level: %ddB (%05d)\n", value >> 8, value);
+
+	/* highest noise level: 32dB */
+	if (value >= 0x2000) {
+		value = 0;
+	} else {
+		value = ~value << 3;
+	}
+
+	goto ret;
+
+	/* Digital mode has SIGNAL LEVEL important and real
+	   noise level is stored in demodulator registers.
+	 */
+digital:
+	/* best signal: -50dB */
+	if (value <= 0x3200) {
+		value = 0xffff;
+	/* minimum: -114dB - should be 0x7200 but real zero is 0x713A */
+	} else if (value >= 0x713A) {
+		value = 0;
+	} else {
+		value = ~(value - 0x3200) << 2;
+	}
+
+ret:
+	*strength = value;
+
+	return rc;
+}
+
 static int xc4000_get_frequency(struct dvb_frontend *fe, u32 *freq)
 {
 	struct xc4000_priv *priv = fe->tuner_priv;
@@ -1559,6 +1644,7 @@ static const struct dvb_tuner_ops xc4000_tuner_ops = {
 	.set_params	   = xc4000_set_params,
 	.set_analog_params = xc4000_set_analog_params,
 	.get_frequency	   = xc4000_get_frequency,
+	.get_rf_strength   = xc4000_get_signal,
 	.get_bandwidth	   = xc4000_get_bandwidth,
 	.get_status	   = xc4000_get_status
 };