Re: Using DT overlays for adding virtual hardware

[Jan Kiszka]

On 2016-06-08 17:17, Mark Rutland wrote:
> 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.

I don't want to write yet another virtual driver but ideally reuse
pci-host-generic. Possibly a dumb question, but bow can I make Linux
instantiate a device node compatible with that driver and with the
desired resources? That's what made me think of overlays.

Thanks,
Jan

-- 
Siemens AG, Corporate Technology, CT RDA ITP SES-DE
Corporate Competence Center Embedded Linux