Re: [Xen-devel] Few Comments on the Xen SMMU ARM code

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hello Manish,

On 11/12/14 18:02, manish jaggi wrote:
> On 11 December 2014 at 02:30, Stefano Stabellini
> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> On Wed, 10 Dec 2014, manish jaggi wrote:
>>> Based on my experience with PCI passthrough code merging, below are
>>> some comments:
>>> Both require a change in code
>>>
>>> a) The current code which is non-pci passthrough requires a devices'
>>> device tree node to be associated with smmu node, if that device has
>>> to be assigned to domU.
>>>
>>> In our system there is no platform device which can be passthough. All
>>> devices (including uart) are enumerated using PCI enumeration.
>>> So the device tree looks like
>>>
>>> pcie0 {
>>> }
>>>
>>> smmu {
>>> mmu-masters = <&pcie0 0x100>;
>>> }
>>>
>>> When dom0 boots pcie is assigned to dom0 and a stream ID 0x100 is
>>> created which later conflicts with a valid device enumerated later
>>>
>>> b) Current xen code and linux code used rb_tree with key as dt_node to
>>> locate a device and its smmu. With an enumerated device there is no
>>> such thing. So this would not work.
>>>
>>>
>>> I need your views how PCI passthrough / Non PCI passthrough code can
>>> coexist with the two points mentioned above ?
>>
>> Hello Manish,
>> it is increasingly difficult to reply to your questions without reading
>> any patches or well written design documents.
> 
> Hi Stefano,
> I am sorry about this. I though this mail was discussing on the
> approach already being taken in the current code and I was just
> pointing out issues. I request you to please read the mail one more
> time.

This is not the first time you asked question about the SMMU driver (see
[1]). As I said, I resynced the SMMU driver to use the same as Linux. So
the PCI support should come nicely.

I haven't send anything yet because I'm still clean up the platform
device passthrough code and not happy with some part of the code.
Anyway, I have pushed a branch passthrough-v2.3 on my personal repo:
http://xenbits.xen.org/gitweb/?p=people/julieng/xen-unstable.git

The SMMU drivers should not change too much (assuming the Maintainers
will be happy my change in the IOMMU interface).

Please take a look and let me know if you need to modified on this new
driver or have any question.

> I suggest you send out
>> your series, then we can move forward from there.
>>
> 
> This is the complete smmu.c file which you can refer for PCI
> passthrough (http://pastebin.com/QDX8fpDu)

It's rather difficult to find your changes in a 2000 lines file where
you have lots of debug and commented code. Furthermore you have some
external definition ( such as extern struct pci_dev pci) which is set
somewhere else.

Can you send the whole series as an RFC which all its dependencies (i.e
Linux, GICv3 ITS...)?

> Just FYI this is not a patch, we are still testing on our board and
> can post a patch only after our testing is complete.

I'm lost... I though PCI passthrough was working for you? So what's the
status of the support?

Regards,

[1] http://lists.xen.org/archives/html/xen-devel/2014-11/msg00018.html

-- 
Julien Grall

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