From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Subject: Re: Problems when using latest git tree to boot xen on
 OMAP5
Date: Wed, 9 Oct 2013 12:29:53 +0100
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To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: Chen Baozi <baozich@gmail.com>, Julien Grall <julien.grall@linaro.org>, List Xen Developer <xen-devel@lists.xen.org>
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On Wed, 9 Oct 2013, Ian Campbell wrote:
> On Wed, 2013-10-09 at 12:15 +0100, Julien Grall wrote:
> > On 10/09/2013 09:11 AM, Ian Campbell wrote:
> > > Rather than whitelisting and mapping disabled devices through perhaps we
> > > should implement them as read 0xf (or 0x0) and write ignore?
> > 
> > We can't assume that these values (0x0 or 0xf) won't affect dom0 behaviour.
> 
> 0xff is what you would typically get back if there was no actual
> hardware present.
> 
> > What about a new quirk to map all disabled device in dom0
> > (PLATFORM_QUIRK_DOM0_MAP_DISABLED_DEVICE)?
> 
> Why is this not the default behaviour?

I think this is not a good idea: it prevents us from assigning one
device directly to a domain other than dom0 from Xen at boot time
(without going through something like PCI passthough).
Also if we really don't want dom0 to use a device, it makes perfect
sense that we don't map the device to it.

I would rather introduce PLATFORM_QUIRK_DOM0_EMULATE_DISABLED_DEVICE
and implement it with a simple write ignore, read 0xff.