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

[Elliott Mitchell <ehem+xen@m5p.com>]

On Fri, Nov 12, 2021 at 10:08:54PM +0000, Julien Grall wrote:
> 
> On Fri, 12 Nov 2021 at 21:15, Elliott Mitchell <ehem+xen@m5p.com> wrote:
> > > > 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.
> 
> Reading through the thread, I agree this is the correct theoretical thing to do.
> However, as already pointed out back then, the effort seems quite big for the
> benefit of a single board (AFAIK none of the other SoC we support
> requires this).

Crucial word I would add to the end of the parenthsized sentence; "yet".
Seems entirely plausible other boards could end up needing this for one
reason or another.  Alternatively this could remove the need for many
platform-specific hacks or could simplify support for many boards all at
once.


> My preference is to introduce a per-platform quirk (I believe Stefano was happy
> with this). The advantage is we could get ACPI support for your board hopefully
> merged quicker.

This could be workable as a temporary workaround.  Longer term I suspect
it might well be rather better to *fully* tackle the issue *now*.
Otherwise this seems likely to turn into a database of board-specific
hacks for hundreds or thousands of devices.

I had left the discussion alone towards the end since I was unsure of
what exactly to target (or look at) for this goal.  I was also thinking
long-term planning pretty well required full support, the question was
merely "When?"


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