Xen portability

["FIXED-TERM Klintefjord Boris (XC-CP/ENG3-SE)" <fixed-term.Boris.Klintefjord@xxxxxxxxxxxx>]

Hi Xen community,

I have a somewhat generic question about portability on Arm platforms.

I have been testing Xen on Armv8 using QEMU (with Linux as Dom0 and
also using OP-TEE), and it works fine. I then started to investigate
how portable Xen is among Arm platforms. According to the Xen wiki[1]
there are not many requirements on the hardware to get Xen to work (it
states that Xen only uses the GIC, generic timers, SMMU and a UART)
assuming one already has a functioning Linux with an appropriate DTB
(device tree).

On another Xen wiki page[2] I further get the impression that adding
Xen should be easy once Linux is up and running. The same page also
lists a number of platforms where Xen has been tested.

So my main question is, does that mean that I can expect Xen to work
with low effort on most Arm devices where I already have a functioning
Linux environment and Xen-compatible hardware (GIC, timers, SMMU,
UART)?

The reason for my doubt is that, I more or less arbitrarily started
looking at the NXP i.MX8MQ evaluation board. It has a DTB in Linux
mainline (arch/arm64/boot/dts/freescale/imx8mq-evk.dts), and it seems
to have a GICv3-compliant GIC which Xen supports. I do not know much
about timers, but the DTB states it has timers with compatible
"arm,armv8-timer" which sounds quite generic. I have not found
anything about SMMU and I probably need some UART driver, but it seems
manageable. However, NXP themselves say that they do not support Xen on
that board, but has support for the i.MX8QM board. They have their own
clone of the Xen git[3] for that board. When looking at that git, I see
that they have done quite a bit of changes to the Xen code, and a lot
of additions in form of new drivers. That gives me the impression that
it is not at all so easy to get Xen to work on any board, contrary to
the impression I got from the Xen wiki pages.

So I want to get a feeling for how much effort is usually required to
get Xen up and running on a new platform. Anyone who has some
experience with this, and what the most important things to look for
are when considering the suitability of a platform for Xen?

[1] 
https://wiki.xenproject.org/wiki/Xen_ARM_with_Virtualization_Extensions_whitepaper#Porting_Xen_to_a_new_SoC
[2] https://wiki.xenproject.org/wiki/Xen_ARM_with_Virtualization_Extensions
[3] https://github.com/nxp-imx/imx-xen