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

[Elliott Mitchell <ehem+xen@xxxxxxx>]

On Mon, Nov 15, 2021 at 10:06:20AM +0000, Bertrand Marquis wrote:
> 
> > On 13 Nov 2021, at 01:03, Elliott Mitchell <ehem+xen@xxxxxxx> wrote:
> > 
> > On Fri, Nov 12, 2021 at 11:00:54PM +0000, Julien Grall wrote:
> >> On Fri, 12 Nov 2021 at 22:32, Elliott Mitchell <ehem+xen@xxxxxxx> wrote:
> >>>> 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.
> >> 
> >> As usual, you have to find a balance between cost vs benefits.
> >> 
> >> If you look at the Device-Tree side, we don' t have many platforms
> >> requiring quirks.
> >> In particular, the DMA is so far strictly limited to a single platform 
> >> (RPI).
> >> So I would be surprised if we suddenly require tons of quirks when using
> >> ACPI.
> > 
> > Presently the DMA quirk would be the only consumer, but there will likely
> > be other consumers later.  Might there be few device-tree quirks due to a
> > short list of platforms?  Might full ACPI support vastly increase
> > Xen/ARM's target audience?  (partially ACPI so complex to support so many
> > varied devices)
> 
> We have been looking at the possibility to have ACPI support in Xen.
> The main problem with that is the cost in lines of code in Xen which would be 
> high
> and as a consequence the maintenance cost would be high.
> So if anything is done it must stay properly limited using ifdefs to make 
> sure people
> needing a ???small??? xen can still have one.
> 
> Now I am on the same side as Julien, I would be very happy to help reviewing 
> if you
> decide to do the work :-)

I'm getting the impression everyone knows Xen/ARM urgently needs full
ACPI/UEFI support, just everyone has figured out adequate short-term
workarounds.  As such everyone keeps making small investments into
keeping their short-term workarounds in place, hoping someone else will
fall on the ACPI/UEFI grenade and save everyone.

This sounds suspiciously like the classic Tragedy of the Commons
situation.


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