Re: ACPI/UEFI support for Xen/ARM status?

[Elliott Mitchell <ehem+xen@xxxxxxx>]

On Fri, Nov 12, 2021 at 05:38:02PM +0000, Julien Grall wrote:
> 
> On 12/11/2021 16:52, Elliott Mitchell wrote:
> > On Fri, Nov 12, 2021 at 04:02:36PM +0000, Julien Grall wrote:
> >>
> >> On 12/11/2021 15:44, Elliott Mitchell wrote:

> >>> Julien Grall and Stefano Stabellini had been proposing doing ACPI table
> >>> parsing in a stub domain, but I'm unaware of the status.  Not finding
> >>> much suggests it hasn't gone very far yet.
> >>
> >> This was a very early proposal in case we needed to parse the DSDT in
> >> Xen. This hasn't been needed so far, hence why this is not implemented
> >> and no-one worked on it.
> >>
> >> I am not very familiar how the framebuffer is detected in ACPI. Can you
> >> provide more details on what exactly you want to parse?
> >>
> >> Alternatively, UEFI is meant to provide an API to access the
> >> framebuffer. Would that be suitable for you?
> > 
> > Last time I tried booting on UEFI, Domain 0 (Linux) was unable to access
> > the framebuffer on this device.  Whereas the same kernel directly on top
> > of UEFI/ACPI was fully able to access the framebuffer (and graphics
> > chip).
> 
> Do you have any log or pointer to any previous discussion about the issue?

https://lists.xenproject.org/archives/html/xen-devel/2020-10/
https://lists.xenproject.org/archives/html/xen-devel/2020-11/

My thread was "Xen on RP4", pretty sure there have been others.  I see
several approaches suggested, but none overtly agreed on.  Seems like the
end sort of amounts to "We really should have ACPI/UEFI support", but no
specific plans.


> > I had been left with the impression the DSDT parsing was going to be
> > needed for Domain 0 to access the framebuffer.  This was found
> > unnecessary for framebuffer access for Domain 0?
> 
> I thought you were asking for using framebuffer in Xen. There is no need 
> for Xen to parse the DSDT if the framebuffer is solely used by Dom0.
> 
> Your problem with the framebuffer is likely not related to the DSDT. But 
> I can't really provide a lot of input until I see the logs.

https://lists.xenproject.org/archives/html/xen-devel/2020-10/msg01841.html

That is more or less a statement of handling of DSDT is the Right(tm)
solution for Domain 0 to have framebuffer on such a platform.  Though
there are plenty of short-term hacks for the issue.


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