drivers: modem: hl78xx: add AT command timeout event and handlers

Add MODEM_HL78XX_EVENT_AT_CMD_TIMEOUT event to distinguish chat scripts
timeouts from other script failures. The chat callback now maps
MODEM_CHAT_SCRIPT_RESULT_TIMEOUT to this new event.

Update state handlers so AT command timeouts trigger the init fail
diagnostic script during startup, and fall back to the power-on pulse in
the init-fail state, similar to existing timeout handling.

This improves error classification and enables more accurate recovery
logic for long-running or stalled AT command exchanges.

Signed-off-by: Zafer SEN <zafersn93@gmail.com>

Author: zafersn

drivers/modem/hl78xx/hl78xx.c

@@ -176,6 +176,8 @@ static const char *hl78xx_event_str(enum hl78xx_event event)
 #endif /* CONFIG_MODEM_HL78XX_AIRVANTAGE */
 	case MODEM_HL78XX_EVENT_MDM_RESTART:
 		return "modem unexpected restart";
+	case MODEM_HL78XX_EVENT_AT_CMD_TIMEOUT:
+		return "AT command timeout";
 	default:
 		return "unknown event";
 	}
@@ -1022,6 +1024,10 @@ static void hl78xx_await_power_on_event_handler(struct hl78xx_data *data, enum h
 		hl78xx_enter_state(data, MODEM_HL78XX_STATE_RUN_INIT_SCRIPT);
 		break;
 
+	case MODEM_HL78XX_EVENT_AT_CMD_TIMEOUT:
+		hl78xx_enter_state(data, MODEM_HL78XX_STATE_RUN_INIT_FAIL_DIAGNOSTIC_SCRIPT);
+		break;
+
 	default:
 		break;
 	}
@@ -1077,6 +1083,7 @@ static void hl78xx_run_init_fail_script_event_handler(struct hl78xx_data *data,
 		}
 		break;
 	case MODEM_HL78XX_EVENT_TIMEOUT:
+	case MODEM_HL78XX_EVENT_AT_CMD_TIMEOUT:
 		if (hl78xx_gpio_is_enabled(&config->mdm_gpio_pwr_on)) {
 			hl78xx_enter_state(data, MODEM_HL78XX_STATE_POWER_ON_PULSE);
 			break;

drivers/modem/hl78xx/hl78xx_chat.c

@@ -325,6 +325,8 @@ void hl78xx_chat_callback_handler(struct modem_chat *chat, enum modem_chat_scrip
 
 	if (result == MODEM_CHAT_SCRIPT_RESULT_SUCCESS) {
 		hl78xx_delegate_event(data, MODEM_HL78XX_EVENT_SCRIPT_SUCCESS);
+	} else if (result == MODEM_CHAT_SCRIPT_RESULT_TIMEOUT) {
+		hl78xx_delegate_event(data, MODEM_HL78XX_EVENT_AT_CMD_TIMEOUT);
 	} else {
 		hl78xx_delegate_event(data, MODEM_HL78XX_EVENT_SCRIPT_FAILED);
 	}