linux-kernel - Re: Using DT overlays for adding virtual hardware

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Date:	Wed, 8 Jun 2016 16:17:46 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
Cc:	devicetree <devicetree@...r.kernel.org>,
	Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jailhouse <jailhouse-dev@...glegroups.com>,
	Måns Rullgård <mans@...x.de>,
	Antonios Motakis <antonios.motakis@...wei.com>
Subject: Re: Using DT overlays for adding virtual hardware

On Wed, Jun 08, 2016 at 04:16:32PM +0200, Jan Kiszka wrote:
> Hi all,
> 
> already started the discussion off-list with Pantelis, but it's better
> done in public:
> 
> I'm currently exploring ways to make Linux recognize dynamically added
> virtual hardware when running under the Jailhouse hypervisor [1]. We
> need to load drivers for inter-partition communication devices that only
> appear after Jailhouse started (which is done from within Linux, i.e.
> long after boot) or when a partition was added later on. Probably, we
> will simply add a virtual PCI host bridge on systems without physical
> PCI and let the IPC device be explored that way (already works on x86).
> Still, that leaves us with hotplug and unplug on hypervisor activation
> and deactivation.

If I've understood correctly you want to use overlays to inject the
virtual PCI host bridge?

Given that you know precisely what you want to inject, I'm not sure I
see the value of using an overlay. 

Is there some reason you can't just create a device without having to go
via an intermediate step? As I understand it, Xen does that for (some)
virtual devices provided to Dom0 and DomU.

Thanks,
Mark.