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[docs] device-driver: add DM subsystem docs and expand INDEX

Add Doxygen pages for RT-Thread device-model drivers: platform/OFW,
DM core (bus, dm, power), clk/regulator/reset/power-domain, PCI/PIC,
Phye, DMA/hwcache, block/SCSI/ATA/NVMe/UFS/SDIO, SCMI, RPMsg,
mailbox, NVMem, NUMA, syscon, thermal, input/LED/IIO/graphic, and
related power/charger/supply docs.
Expand device-driver INDEX.md with ~90 @subpage entries so all new
pages appear in the driver chapter navigation.
Update existing UART/SPI/RTC/pin/framework/dtc pages: UART docs moved
from serial/ to uart/ (uart + uart_dm + uart_earlycon); SPI and RTC
gain DM companion pages; pin links to pin_dm; framework points at DM
topics.
Focus on registration/probe flow and in-tree APIs; no standalone
VirtIO subsystem page (transport code still incomplete).
Test plan: build Doxygen for documentation/ and verify device-driver
INDEX links resolve without missing @ref/@subpage warnings.

Signed-off-by: GuEe-GUI <2991707448@qq.com>

2026-05-28 16:09:55 +08:00

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@page page_device_uart_earlycon UART early console

Early console (before full UART driver)

Early output runs before the normal rt_serial_device / rt_hw_serial_register path: a minimal putc hook is installed from FDT /chosen stdout-path and/or earlycon= in bootargs.

Sources:

8250 / NS16550 / DW APB: components/drivers/serial/device/8250/early.c
Hypervisor console: components/drivers/serial/device/serial-early-hvc.c

Baud/format/base parsing: serial_cfg_from_args, serial_base_from_args in serial_dm.c — see @ref page_device_uart_dm.

8250 earlycon (`early.c`)

Registration

RT_FDT_EARLYCON_EXPORT entries (examples):

Symbol	`earlycon` name	Example compatible
`ns16550`	`uart8250`	`ns16550`, `ns16550a`
`dw8250`	`uart8250`	`snps,dw-apb-uart`
`tegra20`	`uart8250`	`nvidia,tegra20-uart`
`bcm2835aux`	`uart8250`	`brcm,bcm2835-aux-uart`

Bootargs example:

earlycon=uart8250,mmio32,0x10009000,115200n8

The FDT earlycon core passes options into serial8250_early_fdt_setup, which calls serial8250_config then maps MMIO with rt_ioremap_early.

`serial8250_early_putc`

Polls UART LSR (TEMT | THRE) after writing UART_TX—safe with interrupts masked. Installed as con->console_putc.

Lifecycle: `serial8250_early_kick`

`why`	Action
`FDT_EARLYCON_KICK_UPDATE`	`rt_ioremap` full mapping when switching from early to runtime map
`FDT_EARLYCON_KICK_COMPLETED`	`rt_iounmap` early mapping after the platform driver owns the port

If config.baud_rate is zero at setup, firmware already programmed the UART; the code only clears IER.

Divisor

When serial->freq is set, init_serial programs DLL/DLM from freq / (16 * baud_rate).

HVC earlycon (`serial-early-hvc.c`)

RT_FDT_EARLYCON_EXPORT(hvc, "hvc", "vmrt-thread,hvc-console", hvc_early_setup);

hvc_early_setup calls rt_hv_version; on success console_putc → rt_hv_console(c).
No MMIO reg—hypervisor console path.

Handoff to full driver

Earlycon prints via rt_kprintf / console_putc.
Platform probe (e.g. 8250-ofw) maps the same UART, serial_dev_set_name, rt_hw_serial_register → uartN for apps.
Early mapping is released on FDT_EARLYCON_KICK_COMPLETED when the serial core finishes transition.

Do not leave early putc and the full driver writing the same UART without the kick handshake.

Pitfalls

reg-shift: early defaults may differ from DT reg-shift in probe—keep them consistent for your IP.
Options buffer: serial_cfg_from_args may modify the string ( OFW suffix).
RX: early path is TX-only; input needs the full UART driver or another console backend.

3.1 KiB Executable File Raw Blame History

Early console (before full UART driver)

8250 earlycon (early.c)

Registration

serial8250_early_putc

Lifecycle: serial8250_early_kick