linux-kernel - Re: [PATCH] console: Add console=auto option

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Date:   Thu, 16 Aug 2018 11:33:11 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, Mark Salter <msalter@...hat.com>,
        Al Stone <ahs3@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        x86@...nel.org, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Kees Cook <keescook@...omium.org>, linux-pm@...r.kernel.org
Subject: Re: [PATCH] console: Add console=auto option

On Thu, 16 Aug 2018 11:28:24 -0400
Prarit Bhargava <prarit@...hat.com> wrote:

> 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@...hat.com>
> >> Cc: Mark Salter <msalter@...hat.com>
> >> Cc: Al Stone <ahs3@...hat.com>
> >> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> >> Cc: Len Brown <len.brown@...el.com>
> >> Cc: Pavel Machek <pavel@....cz>
> >> Cc: x86@...nel.org
> >> Cc: Petr Mladek <pmladek@...e.com>
> >> Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> >> Cc: Steven Rostedt <rostedt@...dmis.org>
> >> Cc: Kees Cook <keescook@...omium.org>
> >> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> >> Cc: linux-pm@...r.kernel.org
> >> ---
> >>  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?

Are you compiling with ACPI enabled?

It would still compile without it and use the properly prototyped
"weak" function.

-- Steve

> 
> I'll fix it though.
>