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

[Peter Crosthwaite]

On Fri, Oct 26, 2012 at 10:36 PM, 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.
>
> Any chance the access you are seeing is at offset 0x68?
>

0x1a8. which for the opregbase + 0x068 for zynq so probably what you
are thinking about. I think the linux kernel is trying to explicitly
put the device in root mode rather than device mode, but those regs
are unimplemented in EHCI.

Regards,
Peter

> cheers,
>   Gerd
>
>