From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: Problems when using latest git tree to boot xen on
 OMAP5
Date: Wed, 9 Oct 2013 13:01:59 +0100
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To: Stefano Stabellini <stefano.stabellini@eu.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, 2013-10-09 at 12:29 +0100, Stefano Stabellini wrote:
> 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).

No it doesn't, it would just be a default behaviour which would be
overrideable by some new command line option.
 
Note that we don't even go as far as you suggest for PCI passthrough on
x86, where dom0 still sees the device and the hide option is a dom0 one.

> 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.