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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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
...
> 
> Best regards.
> 
> Iurii Konovalenko | Senior Software Engineer
> GlobalLogic
> 
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