Audio: Crossover: User simpler iir_df1_4th() IIR function

This patch changes crossover component to use the optimized
4th order IIR function. The LR4 (Linkwitz-Riley 4th order)
filter bank is hard-coded to 4th order, so this change does
no add restrictions.

The filter bank is used by multiband DRC component. The saving
in three bands configuration in a HiFi5 platform is 5.2 MCPS,
from 90.36 MCPS to 85.17 MCPS.

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

Author: singalsu

src/audio/crossover/crossover.c

@@ -161,6 +161,10 @@ static int crossover_init_coef_lr4(struct sof_eq_iir_biquad *coef,
 {
 	int ret;
 
+	/* Ensure the LR4 can be processed with the simplified 4th order IIR */
+	if (CROSSOVER_LR4_NUM_BIQUADS != SOF_IIR_DF1_4TH_NUM_BIQUADS)
+		return -EINVAL;
+
 	/* Only one set of coefficients is stored in config for both biquads
 	 * in series due to identity. To maintain the structure of
 	 * iir_state_df1, it requires two copies of coefficients in a row.
@@ -190,8 +194,8 @@ static int crossover_init_coef_lr4(struct sof_eq_iir_biquad *coef,
 	if (!lr4->delay)
 		return -ENOMEM;
 
-	lr4->biquads = 2;
-	lr4->biquads_in_series = 2;
+	lr4->biquads = CROSSOVER_LR4_NUM_BIQUADS;
+	lr4->biquads_in_series = CROSSOVER_LR4_NUM_BIQUADS;
 
 	return 0;
 }

src/audio/crossover/crossover.h

@@ -15,6 +15,8 @@
 
 #include "crossover_user.h"
 
+#define CROSSOVER_LR4_NUM_BIQUADS 2
+
 struct comp_buffer;
 struct comp_dev;
 
@@ -122,7 +124,7 @@ static inline int32_t crossover_generic_process_lr4(int32_t in,
 						    struct iir_state_df1 *lr4)
 {
 	/* Cascade two biquads with same coefficients in series. */
-	return iir_df1(lr4, in);
+	return iir_df1_4th(lr4, in);
 }
 
 static inline void crossover_free_config(struct sof_crossover_config **config)