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Xen-ARM EFI/ACPI problems (was: Re: [PATCH 0/4] xen/arm: Unbreak ACPI)

On Mon, Sep 28, 2020 at 10:00:35PM +0900, Masami Hiramatsu wrote:
> I've missed the explanation of the attached patch. This prototype
> patch was also needed for booting up the Xen on my box (for the system
> which has no SPCR).

I'm pretty sure of this on the hardware I'm dealing with, but don't know
about the hardware you're dealing with.

Does your device have a framebuffer?  Have you ever tried/succeeded
booting your device with the framebuffer disabled? (booted with a
HDMI/DVI cable disconnected or the device on the other end *completely*
powered down)

Based upon the back and forth both on xen-devel and some messages which
were split off due to not being general.  An observation I had made a
while ago finally caused me to try recreating it.

On the device I'm on (Raspberry PI 4B with Tianocore -> GRUB -> Xen) I
discovered a SPCR table shows up if I boot with the device the output is
plugged into is powered down.  I'm guessing this causes Tianocore to
advise GRUB/Linux/Xen to boot with a serial console (presenting a Serial
Port Console Redirect table), whereas if the display device is
functioning the absense of SPCR is supposed to indicate console on

This means the ACPI_FAILURE case in acpi_iomem_deny_access() simply needs
to be filled in similar to how it likely is on x86.  Allocate a serial
port for Xen's use as console, present it to domain 0 as hvc0, and hide
it from domain 0.

Next issue for me will be getting the framebuffer operational.
Apparently the Xen-ARM EFI implementation doesn't provide any EFI
variables to domain 0?  Jan Beulich, your name was mentioned as person
likely to have ideas for getting Linux's efifb code operational Xen-ARM.

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