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Date: Fri, 26 Oct 2012 14:36:07 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2 11/11] usb/ehci: Put RAM in undefined
	MMIO regions
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To: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Cc: vineshp@xilinx.com, peter.maydell@linaro.org, qemu-devel@nongnu.org, john.williams@xilinx.com, edgar.iglesias@gmail.com, afaerber@suse.de

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?

cheers,
  Gerd