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

On 2014-06-11 11:00, Ian Campbell wrote:
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

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

D'oh! My mail-foo is weak today. I was reading one thread but somehow
managed to post on a different one. Apologies for the noise. :(


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