Re: [PATCH] console: Add console=auto option

[Prarit Bhargava]

On 08/16/2018 11:09 AM, Greg Kroah-Hartman wrote:
> On Thu, Aug 16, 2018 at 10:10:55AM -0400, 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.
>>
>> Tested on systems with and without an ACPI SPCR.  The following kernel
>> parameters were also tested:
>>
>> console=ttyS0,115200    		works
>> earlycon                		works (early console only)
>> console=auto            		works (full console as expected)
>> no console or earlycon arguments	works (no output as expected)
>>
>> Signed-off-by: Prarit Bhargava <prarit@xxxxxxxxxx>
>> Cc: Mark Salter <msalter@xxxxxxxxxx>
>> Cc: Al Stone <ahs3@xxxxxxxxxx>
>> Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
>> Cc: Len Brown <len.brown@xxxxxxxxx>
>> Cc: Pavel Machek <pavel@xxxxxx>
>> Cc: x86@xxxxxxxxxx
>> Cc: Petr Mladek <pmladek@xxxxxxxx>
>> Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
>> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
>> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> Cc: linux-pm@xxxxxxxxxxxxxxx
>> ---
>>  Documentation/admin-guide/kernel-parameters.txt |  1 +
>>  arch/x86/kernel/acpi/boot.c                     |  5 +++++
>>  include/linux/console.h                         |  1 +
>>  kernel/printk/printk.c                          | 10 ++++++++++
>>  4 files changed, 17 insertions(+)
>>
>> 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
>>  
>>  		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);
>> +}
> 
> <snip>
> 
>> +int arch_console_setup(void);
> 
> Function does not match its prototype :(
> 
> How did you build this successfully?

Weird, it compiles on my system?

I'll fix it though.

P.

>