On Thu 2018-08-16 13:39:01, Prarit Bhargava wrote:
> ACPI may contain an SPCR table that defines a default system console.
> On ARM if the table is present then the SPCR console is enabled by default.
> On x86 the SPCR console is used if 'earlycon' (no parameters) is
> specified as a kernel parameter and is used only as the early console.
> To use the SPCR data as a console a user must boot with 'earlycon',
> grep logs & specify a console= kernel parameter, and then reboot again.
>
> Add 'console=auto' that enables a firmware or hardware console, and on
> x86 enable the SPCR console if 'console=auto' is specified.
I basically like the idea. Just one or two nits below.
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index a32f2a126791..dd057224f33b 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -635,6 +635,7 @@
>
> hvc<n> Use the hypervisor console device <n>. This is for
> both Xen and PowerPC hypervisors.
> + auto [X86] Enable ACPI SPCR console
The "auto" option sounds reasonable. But earlycon does exactly this
when used without no extra options. I prefer to stay consistent
with the existing earlycon behavior.
> If the device connected to the port is not a TTY but a braille
> device, prepend "brl," before the device type, for instance
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index 3b20607d581b..fb2616ba3b21 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -1771,3 +1771,8 @@ void __init arch_reserve_mem_area(acpi_physical_address
> addr, size_t size)
> e820__range_add(addr, size, E820_TYPE_ACPI);
> e820__update_table_print();
> }
> +
> +void __init arch_console_setup(void)
> +{
> + acpi_parse_spcr(false, true);
Just for record. I was curious that this might be called twice
(also from acpi_boot_init(). But it looks safe after all.
The trick is in the two bool parameters. One call allows to
register/enable earlycon and ignores normal console. This other
call does exactly the opposite. I do not see any unwanted side
effects.
Best Regards,
Petr
