google_aec: Don't allocate giant blobs on the heap

The operation of the AEC component uses a single buffer as an internal
heap.  This is very large, over half the available SRAM at component
creation time on MTL.  That's just a poor fit for the heap.  It would
be trivial to create a fragmentation scenario by creating/destroying
components (which happens under user control all the way out in Linux
userspace!) where AEC can't initialize and microphone input breaks.

Longer term we can look at moving this usage back to the heap by
integrating the component's internal allocations with the SOF/Zephyr
heap (which is quite performant), allowing it to make fine-grained
allocations which will work more robustly.

Signed-off-by: Andy Ross <andyross@google.com>

src/audio/google/Kconfig

@@ -61,10 +61,10 @@ config COMP_GOOGLE_RTC_AUDIO_REFERENCE_CHANNEL_MAX
 	  retrieved at runtime, but channels higher than this number
 	  are ignored
 
-config COMP_GOOGLE_RTC_AUDIO_PROCESSING_MEMORY_BUFFER_SIZE_BYTES
+config COMP_GOOGLE_RTC_AUDIO_PROCESSING_MEMORY_BUFFER_SIZE_KB
 	depends on COMP_GOOGLE_RTC_AUDIO_PROCESSING
 	int "Memory buffer size for Google Real Time Communication Audio processing"
-	default 200000
+	default 200
 	help
 	  Sets the size of the memory buffer for the Google real-time
 	  communication audio processing.

src/audio/google/google_rtc_audio_processing.c

@@ -53,6 +53,17 @@ DECLARE_SOF_RT_UUID("google-rtc-audio-processing", google_rtc_audio_processing_u
 DECLARE_TR_CTX(google_rtc_audio_processing_tr, SOF_UUID(google_rtc_audio_processing_uuid),
 			   LOG_LEVEL_INFO);
 
+#if !(defined(__ZEPHYR__) && defined(CONFIG_XTENSA))
+/* Zephyr provides uncached memory for static variables on SMP, but we
+ * are single-core component and know we can safely use the cache for
+ * AEC work.  XTOS SOF is cached by default, so stub the Zephyr API.
+ */
+#define arch_xtensa_cached_ptr(p) (p)
+#endif
+
+static __aligned(PLATFORM_DCACHE_ALIGN)
+uint8_t aec_mem_blob[CONFIG_COMP_GOOGLE_RTC_AUDIO_PROCESSING_MEMORY_BUFFER_SIZE_KB * 1024];
+
 struct google_rtc_audio_processing_comp_data {
 #if CONFIG_IPC_MAJOR_4
 	struct sof_ipc4_aec_config config;
@@ -80,7 +91,6 @@ struct google_rtc_audio_processing_comp_data {
 	int num_capture_channels;
 	GoogleRtcAudioProcessingState *state;
 
-	uint8_t *memory_buffer;
 	struct comp_data_blob_handler *tuning_handler;
 	bool reconfigure;
 	int aec_reference_source;
@@ -413,18 +423,9 @@ static int google_rtc_audio_processing_init(struct processing_module *mod)
 	cd->num_frames = CONFIG_COMP_GOOGLE_RTC_AUDIO_PROCESSING_SAMPLE_RATE_HZ /
 		GOOGLE_RTC_AUDIO_PROCESSING_FREQENCY_TO_PERIOD_FRAMES;
 
-	if (CONFIG_COMP_GOOGLE_RTC_AUDIO_PROCESSING_MEMORY_BUFFER_SIZE_BYTES > 0) {
-		cd->memory_buffer = rballoc(0, SOF_MEM_CAPS_RAM,
-					    CONFIG_COMP_GOOGLE_RTC_AUDIO_PROCESSING_MEMORY_BUFFER_SIZE_BYTES *
-					    sizeof(cd->memory_buffer[0]));
-		if (!cd->memory_buffer) {
-			comp_err(dev, "google_rtc_audio_processing_init: failed to allocate memory buffer");
-			ret = -ENOMEM;
-			goto fail;
-		}
-
-		GoogleRtcAudioProcessingAttachMemoryBuffer(cd->memory_buffer, CONFIG_COMP_GOOGLE_RTC_AUDIO_PROCESSING_MEMORY_BUFFER_SIZE_BYTES);
-	}
+	/* Giant blob of scratch memory. */
+	GoogleRtcAudioProcessingAttachMemoryBuffer(arch_xtensa_cached_ptr(&aec_mem_blob[0]),
+						   sizeof(aec_mem_blob));
 
 	cd->state = GoogleRtcAudioProcessingCreateWithConfig(CONFIG_COMP_GOOGLE_RTC_AUDIO_PROCESSING_SAMPLE_RATE_HZ,
 							     cd->num_capture_channels,
@@ -535,7 +536,6 @@ static int google_rtc_audio_processing_init(struct processing_module *mod)
 			GoogleRtcAudioProcessingFree(cd->state);
 		}
 		GoogleRtcAudioProcessingDetachMemoryBuffer();
-		rfree(cd->memory_buffer);
 #if CONFIG_IPC_MAJOR_4
 		rfree(cd->process_buffer);
 #else
@@ -561,7 +561,6 @@ static int google_rtc_audio_processing_free(struct processing_module *mod)
 #endif
 	rfree(cd->aec_reference_buffer);
 	GoogleRtcAudioProcessingDetachMemoryBuffer();
-	rfree(cd->memory_buffer);
 #if CONFIG_IPC_MAJOR_4
 		rfree(cd->process_buffer);
 #else