Audio: Volume: Add linear ramp coefficient function with fixes

The linear slope coefficient calculation is moved to a separate
function. Two functional changes are done.

- The ramp_coef for channel is set to zero if there is no
  transition for the channel. The ensure of non-zero coefficient
  is only needed if there is a transition that is so slow that
  the slope coefficient would round to zero. If this function is
  called for equal volume and tvolume for channel, the ramp_coef
  remains zero, and not smallest non-zero value.
- The handling of ramp disable with zero initial_ramp is changed
  to similar as for windows fade. The set of coefficient to
  volume delta (a large value for large volume jump) is not correct
  even if it appeared to work. It is a remain from old code where
  ramp was not a function of time but a constant step added.

Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>

src/audio/volume/volume.c

@@ -216,6 +216,9 @@ static const struct comp_zc_func_map zc_func_map[] = {
  */
 static inline int32_t volume_linear_ramp(struct vol_data *cd, int32_t ramp_time, int channel)
 {
+	if (!cd->initial_ramp)
+		return cd->tvolume[channel];
+
 	return cd->rvolume[channel] + ramp_time * cd->ramp_coef[channel];
 }
 #endif
@@ -415,6 +418,59 @@ static int volume_free(struct processing_module *mod)
 	return 0;
 }
 
+static void set_linear_ramp_coef(struct vol_data *cd, int chan, bool constant_rate_ramp)
+{
+	int32_t delta;
+	int32_t delta_abs;
+	int32_t coef;
+
+	if (!cd->initial_ramp)
+		return;
+
+	/* Get volume transition delta and absolute value */
+	delta = cd->tvolume[chan] - cd->volume[chan];
+	if (!delta) {
+		cd->ramp_coef[chan] = 0;
+		return;
+	}
+
+	delta_abs = ABS(delta);
+
+	/* The ramp length (initial_ramp [ms]) describes time of mute
+	 * to vol_max unmuting. Normally the volume ramp has a
+	 * constant linear slope defined this way and variable
+	 * completion time. However in streaming start it is feasible
+	 * to apply the entire topology defined ramp time to unmute to
+	 * any used volume. In this case the ramp rate is not constant.
+	 * Note also the legacy mode without known vol_ramp_range where
+	 * the volume transition always uses the topology defined time.
+	 */
+	if (constant_rate_ramp && cd->vol_ramp_range > 0)
+		coef = cd->vol_ramp_range;
+	else
+		coef = delta_abs;
+
+	/* Divide and round to nearest. Note that there will
+	 * be some accumulated error in ramp time the longer
+	 * the ramp and the smaller the transition is.
+	 */
+	coef = (2 * coef / cd->initial_ramp + 1) >> 1;
+
+	/* Scale coefficient by 1/8, round */
+	coef = ((coef >> 2) + 1) >> 1;
+
+	/* Ensure ramp coefficient is at least min. non-zero
+	 * fractional value.
+	 */
+	coef = MAX(coef, 1);
+
+	/* Invert sign for volume down ramp step */
+	if (delta < 0)
+		coef = -coef;
+
+	cd->ramp_coef[chan] = coef;
+}
+
 /**
  * \brief Sets channel target volume.
  * \param[in,out] mod Volume processing module handle
@@ -429,9 +485,6 @@ int volume_set_chan(struct processing_module *mod, int chan,
 {
 	struct vol_data *cd = module_get_private_data(mod);
 	int32_t v = vol;
-	int32_t delta;
-	int32_t delta_abs;
-	int32_t coef;
 
 	/* Limit received volume gain to MIN..MAX range before applying it.
 	 * MAX is needed for now for the generic C gain arithmetic to prevent
@@ -456,52 +509,9 @@ int volume_set_chan(struct processing_module *mod, int chan,
 	cd->rvolume[chan] = cd->volume[chan];
 	cd->vol_ramp_elapsed_frames = 0;
 
-	/* Check ramp type */
-	if (cd->ramp_type == SOF_VOLUME_LINEAR ||
-	    cd->ramp_type == SOF_VOLUME_LINEAR_ZC) {
-		/* Get volume transition delta and absolute value */
-		delta = cd->tvolume[chan] - cd->volume[chan];
-		delta_abs = ABS(delta);
-
-		/* The ramp length (initial_ramp [ms]) describes time of mute
-		 * to vol_max unmuting. Normally the volume ramp has a
-		 * constant linear slope defined this way and variable
-		 * completion time. However in streaming start it is feasible
-		 * to apply the entire topology defined ramp time to unmute to
-		 * any used volume. In this case the ramp rate is not constant.
-		 * Note also the legacy mode without known vol_ramp_range where
-		 * the volume transition always uses the topology defined time.
-		 */
-		if (cd->initial_ramp > 0) {
-			if (constant_rate_ramp && cd->vol_ramp_range > 0)
-				coef = cd->vol_ramp_range;
-			else
-				coef = delta_abs;
-
-			/* Divide and round to nearest. Note that there will
-			 * be some accumulated error in ramp time the longer
-			 * the ramp and the smaller the transition is.
-			 */
-			coef = (2 * coef / cd->initial_ramp + 1) >> 1;
-		} else {
-			coef = delta_abs;
-		}
-
-		/* Scale coefficient by 1/8, round */
-		coef = ((coef >> 2) + 1) >> 1;
-
-		/* Ensure ramp coefficient is at least min. non-zero
-		 * fractional value.
-		 */
-		coef = MAX(coef, 1);
-
-		/* Invert sign for volume down ramp step */
-		if (delta < 0)
-			coef = -coef;
-
-		cd->ramp_coef[chan] = coef;
-		comp_dbg(mod->dev, "cd->ramp_coef[%d] = %d", chan, cd->ramp_coef[chan]);
-	}
+	/* Ramp type specific initialize */
+	if (cd->ramp_type == SOF_VOLUME_LINEAR || cd->ramp_type == SOF_VOLUME_LINEAR_ZC)
+		set_linear_ramp_coef(cd, chan, constant_rate_ramp);
 
 	return 0;
 }