Re: [Qemu-devel] [PATCH 3/3] target-xtensa: xtfpga: support noMMU cores

[Max Filippov]

On Wed, Sep 30, 2015 at 11:45 PM, Peter Maydell
<address@hidden> wrote:
> On 30 September 2015 at 21:17, Max Filippov <address@hidden> wrote:
>> On Tue, Sep 29, 2015 at 11:42 PM, Peter Maydell
>> <address@hidden> wrote:
>>> On 29 September 2015 at 11:34, Max Filippov <address@hidden> wrote:
>>>> Changing address space layout according to CPU type is what happens
>>>> in actual hardware. There are no user-controllable settings that would
>>>> allow mismatching address space layout and CPU type on XTFPGA
>>>> boards. There's also no SoC level mentioned in the developer guides
>>>> for the corresponding boards. So I'm not sure what you're proposing to do.
>>>
>>> I think this should clearly be different machine models
>>> (possibly implemented using different SoC models).
>>
>> There are already 4 different machine models, lx60, lx200, ml605 and
>> kc705, these are real boards for which bitstreams can be created.
>>
>>> This isn't a
>>> CPU-dependent thing at all, it's just your dev tools are hiding
>>> "change the devices and other board/soc level things" behind a
>>> CPU-type dropdown, which it can get away with because the whole
>>> implementation is in a single FPGA.
>>
>> Why duplicating each machine and then only allowing each CPU to be
>> used with only one variant of each machine? It doesn't match what
>> users do with boards and bitstreams, at all.
>
> Because for QEMU the CPU is really just the CPU. Your other
> random devices don't live in the CPU, even if you're
> programming your FPGA with a single bitstream that's
> got the CPUs and a set of devices in it. You can't push
> that stuff into the CPU model, it should live in the
> board model.

I'm not pushing them into CPU model and they do live in the board
model. After all the changes in question were for the hw/xtensa/xtfpga.c
But the board is made in such way that CPUs with and without MMU
see onboard RAM and peripherals at different physical addresses.
I still can't understand what's wrong with that.

-- 
Thanks.
-- Max