arch/x86/boot/early_serial_console.c

Source file repositories/reference/linux-study-clean/arch/x86/boot/early_serial_console.c

File Facts

System
Linux kernel
Corpus path
arch/x86/boot/early_serial_console.c
Extension
.c
Size
3581 bytes
Lines
155
Domain
Architecture Layer
Bucket
arch/x86
Inferred role
Architecture Layer: implementation source
Status
source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

if (!strncmp(arg, "serial", 6)) {
			port = DEFAULT_SERIAL_PORT;
			pos += 6;
		}

		if (arg[pos] == ',')
			pos++;

		/*
		 * make sure we have
		 *	"serial,0x3f8,115200"
		 *	"serial,ttyS0,115200"
		 *	"ttyS0,115200"
		 */
		if (pos == 7 && !strncmp(arg + pos, "0x", 2)) {
			port = simple_strtoull(arg + pos, &e, 16);
			if (port == 0 || arg + pos == e)
				port = DEFAULT_SERIAL_PORT;
			else
				pos = e - arg;
		} else if (!strncmp(arg + pos, "ttyS", 4)) {
			static const int bases[] = { 0x3f8, 0x2f8 };
			int idx = 0;

			/* += strlen("ttyS"); */
			pos += 4;

			if (arg[pos++] == '1')
				idx = 1;

			port = bases[idx];
		}

		if (arg[pos] == ',')
			pos++;

		baud = simple_strtoull(arg + pos, &e, 0);
		if (baud == 0 || arg + pos == e)
			baud = DEFAULT_BAUD;
	}

	if (port)
		early_serial_init(port, baud);
}

#define BASE_BAUD (1843200/16)
static unsigned int probe_baud(int port)
{
	unsigned char lcr, dll, dlh;
	unsigned int quot;

	lcr = inb(port + LCR);
	outb(lcr | DLAB, port + LCR);
	dll = inb(port + DLL);
	dlh = inb(port + DLH);
	outb(lcr, port + LCR);
	quot = (dlh << 8) | dll;

	return BASE_BAUD / quot;
}

static void parse_console_uart8250(void)
{
	char optstr[64], *options;
	int baud = DEFAULT_BAUD;
	int port = 0;

	/*
	 * console=uart8250,io,0x3f8,115200n8
	 * need to make sure it is last one console !
	 */
	if (cmdline_find_option("console", optstr, sizeof(optstr)) <= 0)
		return;

	options = optstr;

	if (!strncmp(options, "uart8250,io,", 12))
		port = simple_strtoull(options + 12, &options, 0);
	else if (!strncmp(options, "uart,io,", 8))
		port = simple_strtoull(options + 8, &options, 0);
	else
		return;

	if (options && (options[0] == ','))
		baud = simple_strtoull(options + 1, &options, 0);
	else
		baud = probe_baud(port);

	if (port)
		early_serial_init(port, baud);

Annotation

Implementation Notes