Re: [PATCH qemu.git 0/1] hw/arm/virt: add 2x sp804 timer

[Axel Heider]

Peter,


> > For the seL4 specific case, this is currently not possible in
> > the standard configuration. It's only exposed for a special
> > debug and benchmarking configuration.
> It's not clear to me what you mean here -- the generic
> timer in the CPU exists in all configurations, so there
> should be no obstacle to seL4 using it.

Access is not exposed to userland in the standard configuration
and the standard kernel API has no no timeouts besides zero and
infinite. It's a design thing in the end. Nothing that could not
be hacked around or be changed in the design in the long run. But
my goal is not to hack around, but have a "proper" machine
simulation instead. Which basically falls down to having a generic
machine in mainline that has a few more customization options.

> > The really cool customization option would be passing a DTB
> > to QEMU that describes exactly what "virt" machine is to be
> > emulated.
>
> This is a firm "no" -- it sounds on the surface like a good
> idea but it doesn't actually work in practice -- DTB files
> don't provide enough info to be able to build a board from,
> except in some specific restricted situations like the Xilinx
> one.

I can see the point. But what about supporting an overlay DTB
that takes a stripped down virt machine as base? This might avoid
some limitation. In the long run, customization via a DTB seems
still better then adding parameters to the command line. For the
short term, a few more command line options seem good enough.

What is the general feeling about having a more general system
emulation option when it comes to the "virt" machine, and a way
of resolving the usage (and security) conflict with the KVM
usecase.

Axel