media: mb86a20s: make the bit rate estimation function more generic

While 99% of the implementation of the bitrate estimation
routine for ISDB-T is generic, the current approach mangles it
with some mb86a20s-specific thing.

Split the calculus from the specific stuff, in order to make
easier to use the same approach on other drivers requiring
a similar formula.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Sean Young <sean@mess.org>

drivers/media/dvb-frontends/mb86a20s.c

@@ -517,7 +517,7 @@ static void mb86a20s_reset_frontend_cache(struct dvb_frontend *fe)
  * Estimates the bit rate using the per-segment bit rate given by
  * ABNT/NBR 15601 spec (table 4).
  */
-static u32 isdbt_rate[3][5][4] = {
+static const u32 isdbt_rate[3][5][4] = {
 	{	/* DQPSK/QPSK */
 		{  280850,  312060,  330420,  340430 },	/* 1/2 */
 		{  374470,  416080,  440560,  453910 },	/* 2/3 */
@@ -539,21 +539,17 @@ static u32 isdbt_rate[3][5][4] = {
 	}
 };
 
-static void mb86a20s_layer_bitrate(struct dvb_frontend *fe, u32 layer,
-				   u32 modulation, u32 forward_error_correction,
-				   u32 guard_interval,
-				   u32 segment)
+static u32 isdbt_layer_min_bitrate(struct dtv_frontend_properties *c,
+				   u32 layer)
 {
-	struct mb86a20s_state *state = fe->demodulator_priv;
-	u32 rate;
 	int mod, fec, guard;
 
 	/*
 	 * If modulation/fec/guard is not detected, the default is
 	 * to consider the lowest bit rate, to avoid taking too long time
 	 * to get BER.
 	 */
-	switch (modulation) {
+	switch (c->layer[layer].modulation) {
 	case DQPSK:
 	case QPSK:
 	default:
@@ -567,7 +563,7 @@ static void mb86a20s_layer_bitrate(struct dvb_frontend *fe, u32 layer,
 		break;
 	}
 
-	switch (forward_error_correction) {
+	switch (c->layer[layer].fec) {
 	default:
 	case FEC_1_2:
 	case FEC_AUTO:
@@ -587,7 +583,7 @@ static void mb86a20s_layer_bitrate(struct dvb_frontend *fe, u32 layer,
 		break;
 	}
 
-	switch (guard_interval) {
+	switch (c->guard_interval) {
 	default:
 	case GUARD_INTERVAL_1_4:
 		guard = 0;
@@ -603,29 +599,14 @@ static void mb86a20s_layer_bitrate(struct dvb_frontend *fe, u32 layer,
 		break;
 	}
 
-	/* Samples BER at BER_SAMPLING_RATE seconds */
-	rate = isdbt_rate[mod][fec][guard] * segment * BER_SAMPLING_RATE;
-
-	/* Avoids sampling too quickly or to overflow the register */
-	if (rate < 256)
-		rate = 256;
-	else if (rate > (1 << 24) - 1)
-		rate = (1 << 24) - 1;
-
-	dev_dbg(&state->i2c->dev,
-		"%s: layer %c bitrate: %d kbps; counter = %d (0x%06x)\n",
-		__func__, 'A' + layer,
-		segment * isdbt_rate[mod][fec][guard]/1000,
-		rate, rate);
-
-	state->estimated_rate[layer] = rate;
+	return isdbt_rate[mod][fec][guard] * c->layer[layer].segment_count;
 }
 
 static int mb86a20s_get_frontend(struct dvb_frontend *fe)
 {
 	struct mb86a20s_state *state = fe->demodulator_priv;
 	struct dtv_frontend_properties *c = &fe->dtv_property_cache;
-	int layer, rc;
+	int layer, rc, rate, counter;
 
 	dev_dbg(&state->i2c->dev, "%s called.\n", __func__);
 
@@ -676,10 +657,21 @@ static int mb86a20s_get_frontend(struct dvb_frontend *fe)
 		dev_dbg(&state->i2c->dev, "%s: interleaving %d.\n",
 			__func__, rc);
 		c->layer[layer].interleaving = rc;
-		mb86a20s_layer_bitrate(fe, layer, c->layer[layer].modulation,
-				       c->layer[layer].fec,
-				       c->guard_interval,
-				       c->layer[layer].segment_count);
+
+		rate = isdbt_layer_min_bitrate(c, layer);
+		counter = rate * BER_SAMPLING_RATE;
+
+		/* Avoids sampling too quickly or to overflow the register */
+		if (counter < 256)
+			counter = 256;
+		else if (counter > (1 << 24) - 1)
+			counter = (1 << 24) - 1;
+
+		dev_dbg(&state->i2c->dev,
+			"%s: layer %c bitrate: %d kbps; counter = %d (0x%06x)\n",
+			__func__, 'A' + layer, rate / 1000, counter, counter);
+
+		state->estimated_rate[layer] = counter;
 	}
 
 	rc = mb86a20s_writereg(state, 0x6d, 0x84);