Re: [Xen-devel] Question on hvc console init

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Konrad,

On 10/28/2014 04:53 PM, Konrad Rzeszutek Wilk wrote:
> On Tue, Oct 28, 2014 at 05:53:25PM +0200, Iurii Konovalenko wrote:
>> Hello, all!
>>
>> I try to bring up Xen on Renesas Lager board (r8a7790 SoC - R-Car H2).
>> Xen revision is 4.4.
>> I try to run Linux (kernel 3.14 + LTSI patches) as Dom0.
>> In kernel I've found strange behaviour in hvc console init function.
>> In file drivers/tty/hvc/hvc_xen.c in function xen_cons_init(void) sources 
>> are:
>>
>>     if (!xen_domain())
>>         return 0;
>>
>>     if (xen_initial_domain())
>>         ops = &dom0_hvc_ops;
>>     else {
>>
>> xen_domain() and xen_initial_domain() are defined to check
>> xen_domain_type variable. This variable is defined and initialized to
>> XEN_NATIVE in arch/arm/xen/enlighten.c. The real value of this
>> variable is set in same file function xen_guest_init(), that is
>> early_initcall. But eraly_initcall is called later, than
>> console_initcall, that's why in time of running xen_cons_init(void)
>> xen_domain_type is not initialized to correct value and
>> xen_cons_init() does not initialize console, as returns on first check
>> "if (!xen_domain())".
>> It is not critical in normal operation, because we have
>> device_initcall xen_hvc_init() that is called after xen_guest_init(),
>> it initialize hvc. But in case of kernel falls before
>> device_initcall's, we can't see any printouts, that could be useful.
>>
>> Could you please explain, may be using some configs or arguments in
>> command line for kernel, how to enable this early console?
> 
> 
> It is explained in the kernel-parameters.txt 
> (https://www.kernel.org/doc/Documentation/kernel-parameters.txt)
> :
> 
> earlyprintk=  [X86,SH,BLACKFIN,ARM,M68k]
>                       earlyprintk=vga
>                       earlyprintk=efi
>                       earlyprintk=xen
> ...

AFAIK, earlyprintk=xen has never work on ARM. This is because we don't
know that we running on Xen until late.

Regards,

-- 
Julien Grall

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