Re: Device pass through on XEN on ARM

From: Ian Campbell <Ian.Campbell@citrix.com>
To: Gordan Bobic <gordan@bobich.net>
Cc: xen-devel@lists.xen.org
Subject: Re: Device pass through on XEN on ARM
Date: Wed, 11 Jun 2014 11:00:45 +0100	[thread overview]
Message-ID: <1402480845.9727.11.camel@kazak.uk.xensource.com> (raw)
In-Reply-To: <8f7eb6e73289910426e673a3d1a944f7@mail.shatteredsilicon.net>

On Wed, 2014-06-11 at 10:53 +0100, Gordan Bobic wrote:
> On 2014-06-11 10:42, Ian Campbell wrote:
> > On Wed, 2014-06-11 at 11:16 +0200, Khandelwal, Shubham wrote:
> >> 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,
> > 
> > How does it fail? Does it give a fault in the hypervisor or the guest
> > kernel or just silently eat the MMIO writes and not do anything?
> > 
> >>  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.
> > 
> > 0x4xxxxxxx is a RAM region on 4.5 (see the end of
> > xen/include/public/arch-arm.h), I suspect your mmio mapping is being
> > clobbered by a RAM mapping (and therefore that your answer above is
> > "silently does nothing".
> > 
> > Do you need this to be a 1:1 mapping or could you move it to some free
> > space? Most of the low GB is free (but do check arch-arm.h) to be used
> > for MMIO mappings.
> 
> I have a sneaky suspicion that part of the problem is that the
> offending BAR is 16GB in size.

What makes you think that? The region is 4K according to the lines shown
above.

Since you mention BAR (a PCI thing) I've a sneaking suspicious this
isn't the thread you think it is ;-)

Ian.