[media] dib8000: estimate strength in dBm

Better to have Signal strength in dB.
This takes a very rough estimation for the signal strength,
that was calibrated using a Dektec DTA-2111 Gold RF generator
and a Pixelview dib8076 stick.

It estimates the signal strength using a linear equation where:
	- the max is -22.5 dBm, with returns 55953
	- the min is -35.0 dBm, with returns 50110

With -22dBm, the signal strengh is returned as 65535.
Unfortunately, the min strength generated with DTA-2111 is
-35dBm.

It should be noticed that approximating it by a linear equation
is not right. I should probably be splitting it into 0.5 dB
linear segments, in order to get a higher precision, just like
it is done on mb86a20s, but that would force me to add some
attenuators, in order to get dB levels below -35dBm, which is,
btw, strong enough to get signal lock.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Acked-by: Patrick Boettcher <pboettcher@kernellabs.com>

diff --git a/drivers/media/dvb-frontends/dib8000.c b/drivers/media/dvb-frontends/dib8000.c
index 2dbf89365a97a4b39d6f883e8b1e238f2621a907..faf469d1d4379918a965b38b0df4871626cb4513 100644 (file)
--- a/drivers/media/dvb-frontends/dib8000.c
+++ b/drivers/media/dvb-frontends/dib8000.c
@@ -11,6 +11,7 @@
 #include <linux/slab.h>
 #include <linux/i2c.h>
 #include <linux/mutex.h>
+#include <asm/div64.h>
 
 #include "dvb_math.h"
 
@@ -1002,7 +1003,7 @@ static void dib8000_reset_stats(struct dvb_frontend *fe)
        c->post_bit_error.len = 1;
        c->post_bit_count.len = 1;
 
-       c->strength.stat[0].scale = FE_SCALE_RELATIVE;
+       c->strength.stat[0].scale = FE_SCALE_DECIBEL;
        c->strength.stat[0].uvalue = 0;
 
        c->cnr.stat[0].scale = FE_SCALE_NOT_AVAILABLE;
@@ -3847,12 +3848,30 @@ static int dib8000_get_stats(struct dvb_frontend *fe, fe_status_t stat)
        struct dib8000_state *state = fe->demodulator_priv;
        struct dtv_frontend_properties *c = &state->fe[0]->dtv_property_cache;
        int i, lock;
+       u64 tmp;
        u32 snr, val;
        u16 strength;
 
        /* Get Signal strength */
        dib8000_read_signal_strength(fe, &strength);
-       c->strength.stat[0].uvalue = strength;
+
+       /*
+        * Estimate it in dBm
+        * This calculus was empirically determinated by measuring the signal
+        * strength generated by a DTA-2111 RF generator directly connected into
+        * a dib8076 device. The real value can actually be different on other
+        * devices, depending if LNA is enabled or not, if diversity is enabled,
+        * etc.
+        */
+       if (strength == 65535) {
+               c->strength.stat[0].svalue = -22000;
+       } else {
+               tmp = strength * 25000L;
+               do_div(tmp, 11646);
+               c->strength.stat[0].svalue = tmp - 142569;
+               if (c->strength.stat[0].svalue > -22000)
+                       c->strength.stat[0].svalue = -22000;
+       }
 
        /* Check if 1 second was elapsed */
        if (!time_after(jiffies, state->get_stats_time))