Re: [Qemu-arm] [PATCH v3 7/7] raspi: add raspberry pi 2 machine

[Andrew Baumann]

> From: Peter Crosthwaite [mailto:address@hidden
> Sent: Thursday, 14 January 2016 15:35
> 
> On Thu, Jan 14, 2016 at 3:04 PM, Andrew Baumann
> <address@hidden> wrote:
> > Hi Peter,
> >
> >> From: Peter Crosthwaite [mailto:address@hidden
> >> Sent: Tuesday, 12 January 2016 16:44
> >> On Tue, Jan 12, 2016 at 3:53 PM, Andrew Baumann
> >> <address@hidden> wrote:
> >> >> From: Peter Crosthwaite [mailto:address@hidden
> >> >> Sent: Monday, 11 January 2016 19:58
> >> >> > +    /* Allocate and map RAM */
> >> >> > +    memory_region_allocate_system_memory(&s->ram,
> >> >> OBJECT(machine), "ram",
> >> >> > +                                         machine->ram_size);
> >> >> > +
> memory_region_add_subregion_overlap(get_system_memory(), 0,
> >> >> &s->ram, 0);
> >> >>
> >> >> I thought the SoC handled this now? Why do you need to add to
> >> >> system_memory?
> >> >
> >> > If I don't map it here, how do RAM accesses from the CPUs work?
> >> >
> >>
> >> Do the CPUs not have their AS'es connected to your custom ASes by the
> SoC
> >> layer?
> >>
> >> > Or are you saying that I should still do this, but do it in the SoC not 
> >> > the
> >> board level?
> >> >
> >>
> >> I was hoping we could get away with 0 use of system_memory.
> >
> > On further investigation, I don't think it's possible to wire up CPU ASes
> explicitly. There's no obvious property to set. Each cpu->as is initialised to
> point to address_space_memory at the top of cpu_exec_init(), and there is
> no way I could see to override that.
> >
> > I think what I have now is pretty clean, but if you'd prefer to do the
> mapping at into the global AS at SoC level that's fine with me too.
> >
> 
> If it cant be done yet, what is here is a preferable approach. PMM has
> some work on list for CPU ASes that may be realted, moreso for the
> secure attributes though I think.

Ok. It looks like the patch you CCed me on would enable this. But I don't 
really want to wait for that with Pi, and honestly I don't think this is too 
bad -- there are only a handful of things in the system_memory space (the RAM, 
the peripherals blob, and the 2836 multi-core controller on pi2), and it seems 
unlikely to be of great benefit unless some future madman starts building 
multi-pi boards with bizarre mapping schemes. Let's hope not :)

Andrew