Re: [PATCH 0/4] xen/arm: Unbreak ACPI

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Sat, 10 Oct 2020, Julien Grall wrote:
> On 28/09/2020 07:47, Masami Hiramatsu wrote:
> > Hello,
> 
> Hi Masami,
> 
> > This made progress with my Xen boot on DeveloperBox (
> > https://www.96boards.org/product/developerbox/ ) with ACPI.
> > 
> 
> I have reviewed the patch attached and I have a couple of remarks about it.
> 
> The STAO table was originally created to allow an hypervisor to hide devices
> from a controller domain (such as Dom0). If this table is not present, then it
> means the OS/hypervisor can use any device listed in the ACPI table.
> 
> Additionally, the STAO table should never be present in the host ACPI table.
> 
> Therefore, I think the code should not try to find the STAO. Instead, it
> should check whether the SPCR table is present.

Yes, that makes sense, but that brings me to the next question.

SPCR seems to be required by SBBR, however, Masami wrote that he could
boot on a system without SPCR, which gets me very confused for two
reasons:

1) Why there is no SPCR? Isn't it supposed to be mandatory? Is it
because there no UART on Masami's system?

2) If there is no SPCR, how did Masami manage to boot Xen?
I take without any serial output? Just with the framebuffer?