drivers: modem: ublox-sara-r4: constify modem_cmd and setup_cmd structures

Constifying global data allows to save lots of RAM. Defining data inside
function as 'static const' allows on the other hand to save stack usage
and reduced code size (because data doesn't have to be copied on stack
in runtime).

This improvement allows to save 448 bytes of RAM and 88 bytes of ROM
when compiled on ARM, with default configuration.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>

drivers/modem/ublox-sara-r4.c

diff --git a/drivers/modem/ublox-sara-r4.c b/drivers/modem/ublox-sara-r4.c
index 5f6ae28..fb406c1 100644
--- a/drivers/modem/ublox-sara-r4.c
+++ b/drivers/modem/ublox-sara-r4.c
@@ -294,7 +294,7 @@
 /* send binary data via the +USO[ST/WR] commands */
 static ssize_t send_socket_data(struct modem_socket *sock,
 				const struct sockaddr *dst_addr,
-				struct modem_cmd *handler_cmds,
+				const struct modem_cmd *handler_cmds,
 				size_t handler_cmds_len,
 				const char *buf, size_t buf_len,
 				k_timeout_t timeout)
@@ -824,7 +824,7 @@
 #if defined(CONFIG_MODEM_UBLOX_SARA_AUTODETECT_VARIANT)
 static void modem_rssi_query_work(struct k_work *work)
 {
-	struct modem_cmd cmds[] = {
+	static const struct modem_cmd cmds[] = {
 		  MODEM_CMD("+CSQ: ", on_cmd_atcmdinfo_rssi_csq, 2U, ","),
 		  MODEM_CMD("+CESQ: ", on_cmd_atcmdinfo_rssi_cesq, 6U, ","),
 	};
@@ -859,7 +859,7 @@
 #else
 static void modem_rssi_query_work(struct k_work *work)
 {
-	struct modem_cmd cmd =
+	static const struct modem_cmd cmd =
 #if defined(CONFIG_MODEM_UBLOX_SARA_U2)
 		MODEM_CMD("+CSQ: ", on_cmd_atcmdinfo_rssi_csq, 2U, ",");
 	static char *send_cmd = "AT+CSQ";
@@ -889,7 +889,7 @@
 static void modem_reset(void)
 {
 	int ret = 0, retry_count = 0, counter = 0;
-	static struct setup_cmd setup_cmds[] = {
+	static const struct setup_cmd setup_cmds[] = {
 		/* turn off echo */
 		SETUP_CMD_NOHANDLE("ATE0"),
 		/* stop functionality */
@@ -924,7 +924,7 @@
 	};
 
 #if defined(CONFIG_MODEM_UBLOX_SARA_AUTODETECT_VARIANT)
-	static struct setup_cmd post_setup_cmds_u2[] = {
+	static const struct setup_cmd post_setup_cmds_u2[] = {
 #if !defined(CONFIG_MODEM_UBLOX_SARA_AUTODETECT_APN)
 		/* set the APN */
 		SETUP_CMD_NOHANDLE("AT+UPSD=0,1,\""
@@ -937,7 +937,7 @@
 	};
 #endif
 
-	static struct setup_cmd post_setup_cmds[] = {
+	static const struct setup_cmd post_setup_cmds[] = {
 #if defined(CONFIG_MODEM_UBLOX_SARA_U2)
 		/* set the APN */
 		SETUP_CMD_NOHANDLE("AT+UPSD=0,1,\""
@@ -1144,7 +1144,8 @@
 static int create_socket(struct modem_socket *sock, const struct sockaddr *addr)
 {
 	int ret;
-	struct modem_cmd cmd = MODEM_CMD("+USOCR: ", on_cmd_sockcreate, 1U, "");
+	static const struct modem_cmd cmd =
+		MODEM_CMD("+USOCR: ", on_cmd_sockcreate, 1U, "");
 	char buf[sizeof("AT+USOCR=#,#####\r")];
 	uint16_t local_port = 0U, proto = 6U;
 
@@ -1336,7 +1337,7 @@
 {
 	struct modem_socket *sock = (struct modem_socket *)obj;
 	int ret, next_packet_size;
-	struct modem_cmd cmd[] = {
+	static const struct modem_cmd cmd[] = {
 		MODEM_CMD("+USORF: ", on_cmd_sockreadfrom, 4U, ","),
 		MODEM_CMD("+USORD: ", on_cmd_sockread, 2U, ","),
 	};
@@ -1421,7 +1422,7 @@
 {
 	int ret;
 	struct modem_socket *sock = (struct modem_socket *)obj;
-	struct modem_cmd cmd[] = {
+	static const struct modem_cmd cmd[] = {
 		MODEM_CMD("+USOST: ", on_cmd_sockwrite, 2U, ","),
 		MODEM_CMD("+USOWR: ", on_cmd_sockwrite, 2U, ","),
 	};
@@ -1558,7 +1559,8 @@
 			       const struct zsock_addrinfo *hints,
 			       struct zsock_addrinfo **res)
 {
-	struct modem_cmd cmd = MODEM_CMD("+UDNSRN: ", on_cmd_dns, 1U, ",");
+	static const struct modem_cmd cmd =
+		MODEM_CMD("+UDNSRN: ", on_cmd_dns, 1U, ",");
 	uint32_t port = 0U;
 	int ret;
 	/* DNS command + 128 bytes for domain name parameter */
@@ -1696,13 +1698,13 @@
 	.init = modem_net_iface_init,
 };
 
-static struct modem_cmd response_cmds[] = {
+static const struct modem_cmd response_cmds[] = {
 	MODEM_CMD("OK", on_cmd_ok, 0U, ""), /* 3GPP */
 	MODEM_CMD("ERROR", on_cmd_error, 0U, ""), /* 3GPP */
 	MODEM_CMD("+CME ERROR: ", on_cmd_exterror, 1U, ""),
 };
 
-static struct modem_cmd unsol_cmds[] = {
+static const struct modem_cmd unsol_cmds[] = {
 	MODEM_CMD("+UUSOCL: ", on_cmd_socknotifyclose, 1U, ""),
 	MODEM_CMD("+UUSORD: ", on_cmd_socknotifydata, 2U, ","),
 	MODEM_CMD("+UUSORF: ", on_cmd_socknotifydata, 2U, ","),