earlycon

最新推荐文章于 2024-07-28 17:57:55 发布

jinbc

最新推荐文章于 2024-07-28 17:57:55 发布

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CC 4.0 BY-SA版权

文章标签： linux

本文链接：https://blog.youkuaiyun.com/jinbc/article/details/122873867

本文介绍了Linux早期控制台earlycon的配置，包括如何定义串口，以及OF_EARLYCON_DECLARE的作用，它用于记录earlycon地址。在启动过程中，earlycon会根据bootargs中的earlycon参数或console进行初始化。

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首先你需要定义一个对应的串口

OF_EARLYCON_DECLARE(s3c2440, "samsung,s3c2440-uart",
			s3c2440_early_console_setup);

OF_EARLYCON_DECLARE作用主要是在__earlycon_table段记录你earlycon对应的地址，以便后续能够找到。

#define OF_EARLYCON_DECLARE(_name, compat, fn)				\
	_OF_EARLYCON_DECLARE(_name, compat, fn,				\
			     __UNIQUE_ID(__earlycon_##_name))

#define _OF_EARLYCON_DECLARE(_name, compat, fn, unique_id)		\
	static const struct earlycon_id unique_id			\
	     EARLYCON_USED_OR_UNUSED __initconst			\
		= { .name = __stringify(_name),				\
		    .compatible = compat,				\
		    .setup = fn  };					\
	static const struct earlycon_id EARLYCON_USED_OR_UNUSED		\
		__section(__earlycon_table)				\
		* const __PASTE(__p, unique_id) = &unique_id

如何执行？通过bootargs中earlycon参数或者console进入param_setup_earlycon函数

static int __init param_setup_earlycon(char *buf)
{
	int err;

	/*
	 * Just 'earlycon' is a valid param for devicetree earlycons;
	 * don't generate a warning from parse_early_params() in that case
	 */
	if (!buf || !buf[0]) {
		if (IS_ENABLED(CONFIG_ACPI_SPCR_TABLE)) {
			earlycon_init_is_deferred = true;
			return 0;
		} else {
			return early_init_dt_scan_chosen_stdout();
		}
	}

	err = setup_earlycon(buf);
	if (err == -ENOENT || err == -EALREADY)
		return 0;
	return err;
}

int __init setup_earlycon(char *buf)
{
	const struct earlycon_id **p_match;

	if (!buf || !buf[0])
		return -EINVAL;

	if (early_con.flags & CON_ENABLED)
		return -EALREADY;

	for (p_match = __earlycon_table; p_match < __earlycon_table_end;
	     p_match++) {
		const struct earlycon_id *match = *p_match;
		size_t len = strlen(match->name);

		if (strncmp(buf, match->name, len))
			continue;

		if (buf[len]) {
			if (buf[len] != ',')
				continue;
			buf += len + 1;
		} else
			buf = NULL;

		return register_earlycon(buf, match);
	}

	return -ENOENT;
}

static int __init register_earlycon(char *buf, const struct earlycon_id *match)
{
	int err;
	struct uart_port *port = &early_console_dev.port;

	/* On parsing error, pass the options buf to the setup function */
	if (buf && !parse_options(&early_console_dev, buf))
		buf = NULL;

	spin_lock_init(&port->lock);
	port->uartclk = BASE_BAUD * 16;
	if (port->mapbase)
		port->membase = earlycon_map(port->mapbase, 64);

	earlycon_init(&early_console_dev, match->name);
	err = match->setup(&early_console_dev, buf);
	if (err < 0)
		return err;
	if (!early_console_dev.con->write)
		return -ENODEV;
	/* 调用注册控制台 */
	register_console(early_console_dev.con);
	return 0;
}