On Tue, 6 Nov 2018, Peng Fan wrote:
> Hi Julien,
> 
> > -----Original Message-----
> > From: Xen-devel [mailto:xen-devel-bounces@lists.xenproject.org] On Behalf Of
> > Peng Fan
> > Sent: 2018年11月5日 10:11
> > To: Julien Grall <julien.grall@arm.com>; xen-devel@lists.xenproject.org;
> > Stefano Stabellini <sstabellini@kernel.org>
> > Subject: Re: [Xen-devel] Does XEN ARM support RTC in domu?
> > 
> > Hi Julien,
> > 
> > > >>
> > > >>>
> > > >>> Just have a question, does XEN ARM support RTC in domu? To support
> > > >>> Android
> > > >> in DomU, RTC is needed for alarm, but I did not find information
> > > >> about RTC on xen for domu. So this need a new RTC paravirtualization
> > driver?
> > > Any suggestions?
> > > >>
> > > >> By RTC, do you mean Real-Time Clock? Something like PL031? Or do
> > > >> you have something else in mind?
> > > >
> > > > Yes, Real Time Clock like PL031 in DomU. I do not have a good idea
> > > > support RTC in ARM DomU, KVM and XEN x86 seems use emulated RTC in
> > > > qemu. Thinking of paravirtual RTC, and dom0 control the expire time
> > > > for
> > > alarm.
> > >
> > > The PL031 is quite small (based on the QEMU version). So I think it
> > > would be fine to provide an emulation in the hypervisor.
> > 
> > Ok. Just like the hvm x86, implement emulate PL031 inside XEN. I'll give a try.
> 
> Just a follow up question, emulating PL031 in xen, do you have idea how to inject virtual interrupt to domu?
> The interrupt should be only cpu interface interrupt, I think.

Have a loop at the existing virtual timer: xen/arch/arm/vtimer.c
It should give you a decent idea.