Re: [Xen-devel] [PATCH] kernel-parameters: document earlycon=xenboot

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

On Tue, Apr 05, 2016 at 06:16:35PM -0700, Stefano Stabellini wrote:
> On Tue, 5 Apr 2016, Konrad Rzeszutek Wilk wrote:
> > On Tue, Apr 05, 2016 at 11:43:36AM -0400, Chris Patterson wrote:
> > > On Tue, Apr 5, 2016 at 9:49 AM, Konrad Rzeszutek Wilk
> > > <konrad.wilk@xxxxxxxxxx> wrote:
> > > > On Mon, Apr 04, 2016 at 10:48:11PM -0400, Chris Patterson wrote:
> > > >> Add earlycon=xenboot option to Documentation/kernel-parameters.txt.
> > > >>
> > > >
> > > > But it is not true.
> > > >
> > > > I tried this on x86: "earlycon=xenboot console=tty0"
> 
> Was it a PV guest? Do you have SERIAL_EARLYCON enabled in your kconfig?

Yes, dom0 in fact.
> Does Xen allow DomU debug output via HYPERVISOR_console_io in your config?

Yes. That works.
> 
> 
> > > I can investigate further, but hopefully Stefano can chime in more
> > > definitively on what is supported.
> > > 
> > > I used "earlycon=xenboot console=hvc0" with success for dom0 on my
> > > ARM64 platform.
> > 
> > Perhaps the documentation should also have [ARM], like some of the
> > other ones?
> > 
> 
> I don't recall whether I actually tested earlycon on x86, but looking at
> the code it should work, at least for PV guests (you need to be able to
> issue hypercalls and HVM guests cannot do that until they map the
> hypercall page). 
> 
> In any case given that x86 has earlyprintk, specifying
> xenboot as only available for ARM and ARM64 is also OK for me, but I
> would prefer to keep it arch-independent given that earlycon is.

/me nods.

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