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Date: Mon, 10 Jun 2013 20:06:49 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [Qemu-trivial] [PATCH] ioport/memory: check that
 both .read and .write callbacks are defined
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To: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Cc: qemu-trivial@nongnu.org, Michael Tokarev <mjt@tls.msk.ru>, qemu-devel@nongnu.org, =?iso-8859-1?Q?Herv=E9?= Poussineau <hpoussin@reactos.org>, Gerd Hoffmann <kraxel@redhat.com>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>

On Mon, Jun 10, 2013 at 07:14:45PM +1000, Peter Crosthwaite wrote:
> Hi,
> 
> On Mon, Jun 10, 2013 at 3:27 PM, Gerd Hoffmann <kraxel@redhat.com> wrote:
> >   Hi,
> >
> >> Maybe instead (or in addition to), we should provide a dummy
> >> read or write functions -- instead of fixing each such occurence
> >> to use its own dummy function
> >
> > Makes sense, especially for write where we can just ignore what the
> > guest attempts to write.  Not sure we can have a generic handler for
> > reads.  Maybe two, one which returns 0xff and one which returns 0x00.
> >
> 
> FWIW, I have one in my tree that qemu_log(LOG_GUEST_ERROR's such
> accesses that I use for unimplemented devices. It's worthwhile to trap
> such accesses and speaking for the Xilinx LQSPI case, my preference is
> for some form of failure rather than silent write-ignore. And can we
> have an option where a invalid writes have consistent behavior with
> unassigned accesses?
> 
> Regards,
> Peter

Probably not a good idea. Ignoring unassigned addresses
is very handy for compatibility: we can run new guests
on old qemu and They don't crash or log errors.

> > cheers,
> >   Gerd
> >
> >