[media] rtl2830: implement .read_snr()

Reports value as a 0.1 dB.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

2 files changed, 42 insertions, 1 deletions

diff --git a/drivers/media/dvb/frontends/rtl2830.c b/drivers/media/dvb/frontends/rtl2830.c
index 45196c5b0736..e6d7c501717a 100644
--- a/drivers/media/dvb/frontends/rtl2830.c
+++ b/drivers/media/dvb/frontends/rtl2830.c
@@ -404,8 +404,48 @@ err:
 
 static int rtl2830_read_snr(struct dvb_frontend *fe, u16 *snr)
 {
-        *snr = 0;
+        struct rtl2830_priv *priv = fe->demodulator_priv;
+        int ret, hierarchy, constellation;
+        u8 buf[2], tmp;
+        u16 tmp16;
+#define CONSTELLATION_NUM 3
+#define HIERARCHY_NUM 4
+        static const u32 snr_constant[CONSTELLATION_NUM][HIERARCHY_NUM] = {
+                { 70705899, 70705899, 70705899, 70705899 },
+                { 82433173, 82433173, 87483115, 94445660 },
+                { 92888734, 92888734, 95487525, 99770748 },
+        };
+
+        /* reports SNR in resolution of 0.1 dB */
+
+        ret = rtl2830_rd_reg(priv, 0x33c, &tmp);
+        if (ret)
+                goto err;
+
+        constellation = (tmp >> 2) & 0x03; /* [3:2] */
+        if (constellation > CONSTELLATION_NUM - 1)
+                goto err;
+
+        hierarchy = (tmp >> 4) & 0x07; /* [6:4] */
+        if (hierarchy > HIERARCHY_NUM - 1)
+                goto err;
+
+        ret = rtl2830_rd_regs(priv, 0x40c, buf, 2);
+        if (ret)
+                goto err;
+
+        tmp16 = buf[0] << 8 | buf[1];
+
+        if (tmp16)
+                *snr = (snr_constant[constellation][hierarchy] -
+                                intlog10(tmp16)) / ((1 << 24) / 100);
+        else
+                *snr = 0;
+
         return 0;
+err:
+        dbg("%s: failed=%d", __func__, ret);
+        return ret;
 }
 
 static int rtl2830_read_ber(struct dvb_frontend *fe, u32 *ber)
diff --git a/drivers/media/dvb/frontends/rtl2830_priv.h b/drivers/media/dvb/frontends/rtl2830_priv.h
index 4a464761b5b8..9b20557ccf6c 100644
--- a/drivers/media/dvb/frontends/rtl2830_priv.h
+++ b/drivers/media/dvb/frontends/rtl2830_priv.h
@@ -22,6 +22,7 @@
 #define RTL2830_PRIV_H
 
 #include "dvb_frontend.h"
+#include "dvb_math.h"
 #include "rtl2830.h"
 
 #define LOG_PREFIX "rtl2830"