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Re: [Xen-devel] Device pass through on XEN on ARM

On mer, 2014-06-11 at 11:16 +0200, Khandelwal, Shubham wrote:
> On 05/01/2014 08:26 PM, Ian Campbell wrote:

> > Obviously this is all very hacky and as Julien says there are various
> > things in the pipeline for 4.5 which will allow this to be done
> > properly.
> >
> > Ian.
> Hello Ian, Julien,
> Just to try out the passthrough using the hacks you mentioned, I made changes 
> in xen to assign a GPIO controlled LED to domU by calling map_mmio_regions() 
> in the domain creation path. After domU boots, when I try to access the LED 
> using ioremap, ioread and iowrite from kernel space I see that I am not able 
> to control the LED, also when I try to control LED using sysfs from user 
> space it shows 'no such device' error.
> I am using xen 4.5 unstable and I have made the following changes in 
> xen/common/domctl.c :: do_domctl(), after line 473:
> int passthrough = map_mmio_regions(d, 0x4805B000, 0x4805B000 + 0x1000, 
> 0x4805B000);
> if (passthrough)
>         printk("Failed to map passthrough_LED @ 0x4805B000 to dom%d\n", 
> d->domain_id); 
> While booting domU, in the logs I can see there is no error in 
> map_mmio_regions(). Am I missing something here.
May I suggest trying to apply Arianna's series, and see whether that
helps? IIRC, there should even be the possibility of setting up non 1:1
mappings, directly from the config file (uless that got dropped in the
latest versions, which I could not follow closely).

In any case, it look like both less work, and a more tested path (given
the amount of attention and review the series is getting). It also would
be greeat to have some more testing of the series itself, not to mention
that, if it works, you'll be all set for when the series will go
upstream! :-P

I believe the last version of Arianna's series is this one:

Just 2 cents... :-)


<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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