Re: [Xen-devel] [RFC PATCH 00/19] xen/arm: Add ITS support

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

Hi Julien,

On Mon, Mar 9, 2015 at 11:46 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> Hello Vijay,
>
> On 09/03/2015 14:57, Vijay Kilari wrote:
>>
>> On Tue, Mar 3, 2015 at 5:13 PM, Julien Grall <julien.grall@xxxxxxxxxx>
>> wrote:
>>>
>>> Hello Vijay,
>>>
>>> On 03/03/2015 03:55, Vijay Kilari wrote:
>>>>
>>>>
>>>> On Mon, Mar 2, 2015 at 6:49 PM, Julien Grall <julien.grall@xxxxxxxxxx>
>>>> wrote:
>>>>>
>>>>>
>>>>> On 02/03/15 12:30, vijay.kilari@xxxxxxxxx wrote:
>>>>>>
>>>>>>
>>>>>> From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxxxxxxxxxx>
>>>>>>
>>>>>> Add ITS support for arm. Following major features
>>>>>> are supported
>>>>>>    - GICv3 ITS support for arm64 platform
>>>>>>    - Supports only single ITS node
>>>>>
>>>>>
>>>>>
>>>>> Why only one ITS node supported? I though Cavium was using 2 ITS...
>>>>
>>>>
>>>>
>>>> I will update for 2 ITS nodes later when NUMA is supported
>>>
>>>
>>>
>>> Why do you speak about NUMA? AFAICT, there is no requirement to support
>>> NUMA
>>> for having multiple ITS...
>>>
>>> With multiple ITS support, your vITS emulation will likely heavily
>>> change.
>>> So it would be nice to have this support as soon as possible.
>>
>>
>> Incremental changes (as separate patch series)
>> would be more meaningful. I will have a look at it
>> and if possible I will incorporate in next series
>
>
> It doesn't make sense to not support multiple ITS from the beginning.
>
> FWIW, your code is based on the Linux driver which support multiple ITS. So
> why did you drop this support?
>
> Anyway, I'm pretty sure you will have to rework the vITS with the support of
> multiple ITS... Having a separate patch means more work for all of us: more
> series and more review.
>

The changes that I envisage for supporting Multiple ITS is
  - Generate as many number of ITS dt nodes for Dom0 that host DT contains.
  - For DomU always generate only one ITS node
  - vITS will register MMIO handlers for all physical ITS of Dom0, but
vITS will only have
    one VITS structure per domain. The limitation with this approach
is that all vITS requests are
    serialized even though there are more than one physical ITS. But
this approach makes
    implementation simple.
 - The right Physical ITS node command queue is chosen based on device
id in the ITS commands.
   However few commands like MAPC, SYNC & INVALL does not have device
id. These commands
   needs special handling by either consume in vITS or send based on
Collection and Target address mapped.

Regards
Vijay

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