UART / serial DM helpers

Kconfig uses **RT_USING_SERIAL**; registered device names are **uart0**, **uart1**, … Implementation directory: **components/drivers/serial/** (serial core + controller drivers).

Piece	Built when	Source
Serial framework	`RT_USING_SERIAL`	`dev_serial.c` or `dev_serial_v2.c`
DM naming / bootargs parse	`RT_USING_DM`	`serial_dm.c`
OFW platform drivers (8250, PL011, …)	`RT_USING_DM` + `RT_USING_SERIAL`	`serial/device/*` (`host/Kconfig`)

Header: **components/drivers/include/drivers/serial_dm.h**.

Application **rt_device_find("uart2")** usage: UART. Early TX before probe: UART early console.

<tt>serial_dev_set_name</tt>

int serial_dev_set_name(struct rt_serial_device *sdev);

rt_serial_device

serial device structure

Definition: dev_serial.h:254

With **RT_USING_OFW**, tries DTS alias id for **serial** then **uart** on **sdev->parent.ofw_node**.
Otherwise uses an atomic counter seeded from **rt_ofw_get_alias_last_id("serial")** / **uart** so extra ports do not collide with aliased indices.
Sets the parent **rt_device** name to **uartu** via **rt_dm_dev_set_name**.

**INIT_PLATFORM_EXPORT(serial_dm_naming_framework_init)** runs before platform UART probes to initialize **uid_min**.

Prefer **aliases { serial0 = &uart0 }** or **uart0 = &…** in DTS so names match board docs and FinSH/console scripts.

Boot argument parsing

<tt>serial_cfg_from_args</tt>

struct serial_configure serial_cfg_from_args(char *str);

Parses the earlycon / console option tail (after the MMIO base in **earlycon=** strings):

Segment	Meaning
Leading digits	Baud rate (default from `RT_SERIAL_CONFIG_DEFAULT` if missing)
`n` / `o` / `e`	Parity none / odd / even
One digit	Data bits
`r`	RTS/CTS (`RT_SERIAL_FLOWCONTROL_CTSRTS`)

Example: **115200n8** → 115200, no parity, 8 data bits.

If the string ends with the four-byte suffix **OFW**, that marker is cleared—firmware earlycon handoff so the full driver does not re-parse stale bootargs text. Pass a writable buffer when this path is used.

<tt>serial_base_from_args</tt>

void *serial_base_from_args(char *str);

Finds **0x** in the option string and parses a hexadecimal physical base for early bring-up (before OFW **iomap**).

<tt>serial_for_each_args</tt>

Macro to iterate comma-separated sub-arguments in a boot string (multi-earlycon lists).

Typical platform <tt>probe</tt> (8250 / PL011)

Map registers: **rt_ofw_iomap(np, 0)** or **rt_dm_dev_iomap(dev, 0)** (driver-specific).
**rt_ofw_get_irq** / **rt_dm_dev_get_irq** for the interrupt line.
Optional **rt_clk_get**, **rt_reset_control_get**, **current-speed**, **reg-shift** from DT.
Fill **struct rt_serial_device** / SoC wrapper, **serial_dev_set_name** (often inside **serial8250_setup** / driver setup).
**rt_hw_serial_register(&serial->parent, name, flags, priv)** — exposes **uartN** to applications.

Example OFW 8250: **components/drivers/serial/device/8250/8250-ofw.c**, **core.c** (serial8250_setup).

RX DMA: request a channel from DMA engine; completion feeds the serial ISR (**rt_hw_serial_isr**, events **RT_SERIAL_EVENT_RX_DMADONE**).

Pitfalls

Alias vs probe order: ports without aliases get **uart0**, **uart1** in registration order—not always DTS label order.
Pinctrl: apply **pinctrl-0** (or board init) before first TX—see Pin control (pinctrl).
Console vs app: reopening the shell UART can conflict—document exclusive use or use Serial V2 policy if enabled (**RT_USING_SERIAL_V2**).
**RT_DEVICE_CTRL_CONFIG**: must reach hardware in the driver **control** / **configure** path or users see wrong baud after open.