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

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Elliott,

> 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 do concede a device-quirk is reasonable for the short-term.  Presently
> I don't know where to look for better matching targets, so I'm trapped in
> a cave with no light.

What is your need exactly ? A target with frame buffer support ?

Regards
Bertrand

> 
> 
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