在acpi_boot_table_init 中會調用parse_spcr 來從SPCR表中parse console參數，這就不用通過在cmdline中傳遞了。
這個函數首先acpi_get_table_with_size 得到SPCR，然後根據table->interface_type 得到iotype。再根據table->baud_rate得到波特率。
int __init parse_spcr(bool earlycon)
{
status = acpi_get_table_with_size(ACPI_SIG_SPCR, 0,
(struct acpi_table_header **)&table,
&table_size);
switch (table->interface_type) {
case ACPI_DBG2_ARM_SBSA_32BIT:
iotype = "mmio32";
case ACPI_DBG2_ARM_PL011:
case ACPI_DBG2_ARM_SBSA_GENERIC:
case ACPI_DBG2_BCM2835:
uart = "pl011";
break;
case ACPI_DBG2_16550_COMPATIBLE:
case ACPI_DBG2_16550_SUBSET:
if (table->serial_port.space_id ==
ACPI_ADR_SPACE_SYSTEM_MEMORY &&
table->serial_port.bit_width == 32)
iotype = "mmio32";
uart = "uart";
break;
default:
err = -ENOENT;
goto done;
}
switch (table->baud_rate) {
case 3:
baud_rate = 9600;
break;
case 4:
baud_rate = 19200;
break;
case 6:
baud_rate = 57600;
break;
case 7:
baud_rate = 115200;
break;
default:
err = -ENOENT;
goto done;
}
snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d", uart, iotype,
table->serial_port.address, baud_rate);
pr_info("console: %s\n", opts);
if (earlycon)
setup_earlycon(opts);
err = add_preferred_console(uart, 0, opts + strlen(uart) + 1);
done:
early_acpi_os_unmap_memory((void __iomem *)table, table_size);
return err;
}
最後通過snprintf來客制化opts。如果有定義earlycon的話，調用setup_earlycon來初始化earlycon。最後調用add_preferred_console來設定序列槽
add_preferred_console->__add_preferred_console
static int __add_preferred_console(char *name, int idx, char *options,
char *brl_options)
{
struct console_cmdline *c;
int i;
for (i = 0, c = console_cmdline;
i < MAX_CMDLINECONSOLES && c->name[0];
i++, c++) {
if (strcmp(c->name, name) == 0 && c->index == idx) {
if (!brl_options)
selected_console = i;
return 0;
}
}
if (i == MAX_CMDLINECONSOLES)
return -E2BIG;
if (!brl_options)
selected_console = i;
strlcpy(c->name, name, sizeof(c->name));
c->options = options;
braille_set_options(c, brl_options);
c->index = idx;
return 0;
}
最後在__add_preferred_console函數中比較console_cmdline 這個數組中已經注冊的console和apci表傳遞過來的表中的name像比較，如果相等的話，就給selected_console指派，表示用這個來序列槽來輸出log