app: Use C library malloc() instead of System heap.

When following Kconfig variables are set:
CONFIG_COMMON_LIBC_MALLOC=y
CONFIG_COMMON_LIBC_MALLOC_ARENA_SIZE=-1

It uses all remaining RAM for heap that is used by C library.
This is better for us, than trying to guess a static size beforehand.

We still need some amount of system heap for k_malloc(), as at least
nRF Cloud libraries seem to be using that.

Signed-off-by: Seppo Takalo <seppo.takalo@nordicsemi.no>

Author: SeppoTakalo

app/Kconfig

@@ -250,6 +250,15 @@ config SM_NRF_CLOUD
 	default y
 	select EXPERIMENTAL
 
+if SM_NRF_CLOUD
+config HEAP_MEM_POOL_ADD_SIZE_SM_NRF_CLOUD
+	int "Additional heap memory pool size for nRF Cloud support"
+	default 2048
+	help
+	  Some libraries used by nRF Cloud use System Heap (k_malloc() / k_free()) for
+	  dynamic memory allocation.
+endif # SM_NRF_CLOUD
+
 config SM_MQTTC
 	bool "MQTT client support"
 	default y
@@ -298,15 +307,6 @@ config SM_MODEM_PIPE_TIMEOUT
 
 endif # SM_CMUX || SM_PPP
 
-config HEAP_MEM_POOL_ADD_SIZE_SM_AT
-	int "Additional heap memory pool size for AT Host"
-	default 16384 if SM_CMUX
-	default 8192
-	help
-	  Additional heap memory pool size required for AT Host.
-	  This value is added to the total heap memory pool size defined in
-	  CONFIG_HEAP_MEM_POOL_SIZE.
-
 if SM_MQTTC
 
 config SM_MQTTC_MESSAGE_BUFFER_LEN

app/prj.conf

@@ -64,6 +64,8 @@ CONFIG_UART_INTERRUPT_DRIVEN=n
 CONFIG_MAIN_STACK_SIZE=4096
 CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=4096
 CONFIG_AT_MONITOR_HEAP_SIZE=4096
+CONFIG_COMMON_LIBC_MALLOC=y
+CONFIG_COMMON_LIBC_MALLOC_ARENA_SIZE=-1
 
 # Device power management
 CONFIG_PM_DEVICE=y

app/src/sm_at_host.c

@@ -534,7 +534,7 @@ static bool set_sm_mode(struct sm_at_host_ctx *ctx, enum sm_operation_mode mode)
 			if (ctx->data_rb_buf == NULL) {
 				LOG_DBG("Allocating datamode buffer of size %d",
 					CONFIG_SM_DATAMODE_BUF_SIZE);
-				ctx->data_rb_buf = k_malloc(CONFIG_SM_DATAMODE_BUF_SIZE);
+				ctx->data_rb_buf = malloc(CONFIG_SM_DATAMODE_BUF_SIZE);
 				if (ctx->data_rb_buf == NULL) {
 					LOG_ERR("Failed to allocate datamode buffer");
 					return false;
@@ -1128,7 +1128,7 @@ static size_t cmd_rx_handler(struct sm_at_host_ctx *ctx, uint8_t c)
 			rsp_send_error();
 			goto cmd_finnish_or_fail;
 		}
-		uint8_t *new_buf = k_realloc(ctx->at_buf, new_size);
+		uint8_t *new_buf = realloc(ctx->at_buf, new_size);
 
 		if (!new_buf) {
 			LOG_ERR("Failed to expand AT command buffer");
@@ -1261,7 +1261,7 @@ static size_t cmd_rx_handler(struct sm_at_host_ctx *ctx, uint8_t c)
 		ctx->echo_len = 0;
 		/* Release extra AT buffer */
 		if (ctx->at_buf_size > AT_BUF_MIN_SIZE) {
-			uint8_t *new_buf = k_realloc(ctx->at_buf, AT_BUF_MIN_SIZE);
+			uint8_t *new_buf = realloc(ctx->at_buf, AT_BUF_MIN_SIZE);
 
 			if (new_buf) {
 				ctx->at_buf = new_buf;
@@ -1660,7 +1660,7 @@ static int sm_at_host_ctx_init(struct sm_at_host_ctx *ctx, struct modem_pipe *pi
 	/* Initialize context structure */
 	memset(ctx, 0, sizeof(*ctx));
 
-	ctx->at_buf = k_malloc(AT_BUF_MIN_SIZE);
+	ctx->at_buf = malloc(AT_BUF_MIN_SIZE);
 	if (!ctx->at_buf) {
 		LOG_ERR("Failed to allocate AT command buffer");
 		return -ENOMEM;
@@ -1709,7 +1709,7 @@ static struct sm_at_host_ctx *sm_at_host_create(struct modem_pipe *pipe)
 	}
 
 	/* Allocate new instance from heap */
-	ctx = k_malloc(sizeof(*ctx));
+	ctx = malloc(sizeof(*ctx));
 	if (!ctx) {
 		LOG_ERR("Failed to allocate AT host context");
 		return NULL;
@@ -1718,7 +1718,7 @@ static struct sm_at_host_ctx *sm_at_host_create(struct modem_pipe *pipe)
 	/* Initialize the context */
 	err = sm_at_host_ctx_init(ctx, pipe);
 	if (err) {
-		k_free(ctx);
+		free(ctx);
 		return NULL;
 	}
 
@@ -1876,12 +1876,13 @@ static int sm_at_host_destroy(struct sm_at_host_ctx *ctx)
 	/* Remove from instance list */
 	sys_slist_find_and_remove(&instance_list, &ctx->node);
 
+	LOG_INF("Destroyed AT host instance %p", (void *)ctx);
+
 	/* Free the context */
-	k_free(ctx->data_rb_buf);
-	k_free(ctx->at_buf);
-	k_free(ctx);
+	free(ctx->data_rb_buf);
+	free(ctx->at_buf);
+	free(ctx);
 
-	LOG_INF("Destroyed AT host instance %p", (void *)ctx);
 	return 0;
 }