Re: [Qemu-devel] [PATCH v1 8/8] usb/ehci: Put RAM in undefined MMIO regions

[Peter Maydell]

On 25 October 2012 14:21, Avi Kivity <address@hidden> wrote:
> On 10/25/2012 03:12 PM, Peter Maydell wrote:
>>  (2) what should the memory system do for accesses where there is
>>  no memory region? This is really system specific as it depends
>>  what the bus fabric does. For ARM the usual thing would be to
>>  generate a decode error response which will result in the guest
>>  CPU taking a data abort or prefetch abort. I don't think our
>>  memory system currently has any way of saying "for this access
>>  generate an exception"...
>>
>
> You could easily have the top-level container have ->ops that generate
> an exception.

Ah, yes, there's an 'accepts' callback. (That's kind of awkward
as an API because it means your decode logic gets spread between
read, write and accept: there are some devices where it would be
nice to have the 'default:' case of the address switch say "unknown
offset, raise decode error". If the read callback took a uint64_t*
rather than returning the read data, we could make both read and
write return a success/decode-error type of status result.)

-- PMM