Re: [Qemu-devel] [PATCH v2 11/11] usb/ehci: Put RAM in undefined MMIO regions

[Peter Crosthwaite]

On Fri, Oct 26, 2012 at 10:39 PM, Peter Maydell
<address@hidden> wrote:
> On 26 October 2012 13:36, Gerd Hoffmann <address@hidden> wrote:
>> On 10/26/12 07:47, Peter Crosthwaite wrote:
>>> Just put RAM regions in the unimplemented spaces in the MMIO region. These
>>> regions have undefined behaviour, but this at least stops QEMU from 
>>> segfaulting
>>> when the guest bangs on these registers (and sucessfully fakes reading and
>>> writing the registers with no side effects).
>>
>> Make that an io region, have the read() handler return 0xff, write
>> handler do nothing except maybe logging/tracing the access for debugging
>> purposes.  That is more correct for unassigned mmio space than backing
>> by memory.  Adding memory also breaks migration btw.
>>
>> I somehow still think this should be handled one layer up (i.e. the
>> parent region) which could do the approximate arch-specific action.
>
> If it's really in the memory space of the device itself then our device
> model should be handling it.
>

Yeh I admit patch is a hack and ultimately out of scope of this
series. Im going to drop it and put it on my workarounds branch for
the moment (wont appear in v3). Ill get you guys that segfault info,
and see if Gerd has any insights on what the device should actually
do.

Regards,
Peter

> -- PMM
>