cellular_modem : modem_chat_run_script and simple single AT sending and receiving possible?

[MY201314MY]

Describe the bug

the example cellular_modem can run very well in my platform.(Of course I modified my device tree)

I'm not sure if this is a bug. But in fact, I don't want to run AT commands asynchronously. More often, I pay attention to the running results of AT, so I changed it as follow(modem_chat_run_script_async(&data->chat, config->init_chat_script); to modem_chat_run_script(&data->chat, config->init_chat_script);), but it seems that the AT command cannot be send after the change. Are there any steps I'm missing?I'm using STM32F4 Discovery(STM32F407VGT6)

To Reproduce
Steps to reproduce the behavior:

1. copy cellular_modem example
2. west build -b stm32f4_disco -p
3. west flash
4. watch
   
   

After debugging, I found that although k_work_submit(&chat->script_run_work); was called, the corresponding callback static void modem_chat_script_run_handler(struct k_work *item) could never be called.

Although gsm_ppp.c has been abandoned, I think it's AT sending, receiving and parsing is more convenient and concise than the current chat script method. In many cases in my projects, I only need to send one AT command, and the parameters of the AT command can be changed dynamically. Yes, I hope to just adapt the original AT transceiver function to the new modem cellular, but I am not sure whether this is possible.Of course I want to use the new modem_cmux and modem_pipe.

/**
 * @brief  send AT command to interface w/ a TX lock
 *
 * @param  iface: interface to use
 * @param  handler: command handler to use
 * @param  handler_cmds: commands to attach
 * @param  handler_cmds_len: size of commands array
 * @param  buf: NULL terminated send buffer
 * @param  sem: wait for response semaphore
 * @param  timeout: timeout of command
 *
 * @retval 0 if ok, < 0 if error.
 */
static inline int modem_cmd_send(struct modem_iface *iface,
				 struct modem_cmd_handler *handler,
				 const struct modem_cmd *handler_cmds,
				 size_t handler_cmds_len, const uint8_t *buf,
				 struct k_sem *sem, k_timeout_t timeout)
{
	return modem_cmd_send_ext(iface, handler, handler_cmds,
				  handler_cmds_len, buf, sem, timeout, 0);
}```

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[bjarki-andreasen]

Hi, the entire modem subsystem, including the modem_cellular driver is asynchronous. All modules and the driver itself are run using a single thread, the system workqueue thread, using work items.

If you block the work queue, by using a non async function, it will deadlock. The change you are making here is blocking the work queue, which then blocks all other modem modules, so it will never complete.

You can rewrite the driver to be sync, by for example creating a dedicated work queue for it, but this requires more resources :)

To see an example of how the modem modules are used sync, see https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/gnss/gnss_quectel_lcx6g.c

[MY201314MY]

Thank you very much and for your hard work. @bjarki-trackunit

I have completed setting up the module's APN using the asynchronous APIs.
Even the reading and writing of the modem's file system, which is very different for each manufacturer, but the modem can usually provide a file system that is very large compared to the MCU.

typedef struct {
	int(*query_modem_rssi)(int *rssi);
	int(*get_modem_sim_status)(char **status);
	int(*get_modem_sim_eid)(char **eid);
	int(*get_modem_sim_iccid)(char **iccid);

	int(*get_modem_chosen_operator)(char **operator);

	int(*get_modem_rf_status)(int *rf_status);
	int(*set_modem_rf_status)(int rf_status);

	int(*get_modem_access_tech)(int *access);
	int(*set_modem_access_tech)(cellular_access_tech_t access);

	int(*get_modem_pdp)(uint8_t cid, char **type, char **apn);
	int(*set_modem_pdp)(uint8_t cid, char *type, char *apn);

	int(*get_modem_cell_info)(cell_infor_t *p);

	int(*attach_to_network)(k_timeout_t timeout);
} cellular_api_t;

Application can set and get by the driver api argument, I'm not sure if it's suitable.As I known there're some plan to provide some api(s) like this:https://github.com/zephyrproject-rtos/zephyr/blob/cc4d82eeb2d4dd05c571b14e0ffc537167d83e3f/include/zephyr/drivers/cellular.h