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

[Peter Crosthwaite <crosthwaitepeter@gmail.com>]

On Thu, Jan 14, 2016 at 4:43 PM, Andrew Baumann
<Andrew.Baumann@microsoft.com> wrote:
>> From: Peter Crosthwaite [mailto:crosthwaitepeter@gmail.com]
>> Sent: Thursday, 14 January 2016 15:35
>>
>> On Thu, Jan 14, 2016 at 3:04 PM, Andrew Baumann
>> <Andrew.Baumann@microsoft.com> wrote:
>> > Hi Peter,
>> >
>> >> From: Peter Crosthwaite [mailto:crosthwaitepeter@gmail.com]
>> >> Sent: Tuesday, 12 January 2016 16:44
>> >> On Tue, Jan 12, 2016 at 3:53 PM, Andrew Baumann
>> >> <Andrew.Baumann@microsoft.com> wrote:
>> >> >> From: Peter Crosthwaite [mailto:crosthwaitepeter@gmail.com]
>> >> >> 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 :)
>

Agree

Regards,
Peter

> Andrew