Re: [Xen-devel] [RFC PATCH v2 13/22] xen/arm: its: Add virtual ITS command support

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

On Mon, May 4, 2015 at 6:34 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
>
>
> On 04/05/2015 13:58, Vijay Kilari wrote:
>>
>> On Thu, Apr 30, 2015 at 7:59 PM, Julien Grall <julien.grall@xxxxxxxxxx>
>> wrote:
>>>
>>> Hi,
>>>
>>> On 30/04/15 14:47, Stefano Stabellini wrote:
>>>>>>>
>>>>>>>
>>>>>>> If the devid is not within this range, the ITS won't recognize the
>>>>>>> value and
>>>>>>> won't be able to send the interrupt.
>>>>>>>
>>>>>>> So this is clearly not the right value.
>>>>>>
>>>>>>
>>>>>> Sure, in that case the maximum value allowed by GITS_TYPER.Devbits.
>>>>>> Vijay, what is the value of GITS_TYPER.Devbits on your platform?
>>>>>
>>>>>
>>>>> It is 21 bits
>>>>
>>>>
>>>> I would imagine that 21 bits would be plenty to find an unused devid.
>>>>
>>>> Alternatively we could use an inexistent function of a real device, such
>>>> as 00:00.1 (function 1 of the host bridge).
>>>
>>>
>>> As discussed IRL, this idea sounds good to me.
>>>
>>> Although I would be happy with any other way which ensure the devid is
>>> free.
>>
>>
>> Has prototyped with 00.00.1 as device id. But I see that Dom0 boot is
>> slow compared to polling mode. This could be because Dom0 has to keep
>> trapping on creader to check if creader is updated or not.
>
>
> How did you implement the interrupt mode? Could it be improve?

   1) In physical ITS driver its_device is created with devID 00:00.1 with
256 MSI-x are reserved and is named as completion_dev, which is global.

   2) In Domain init,
         - one irq (called completion_irq) is allocated per domain for
this device
           and irq desc is allocated to this domain. This way we can get vITS
           context when interrupt is received.
         - An array of 32 requests(its_requests) is allocated which stores all
           the information about the ITS commands that are converted and written
           to physical ITS queue and each request info contains
           [CReader vITS] [CWriter vITS] [Physical Q Index] [Number of commands]
            [Completion irq] [ status ]

   3) When vITS received ITS command. This command is converted to physical
      command  and written to physical queue, INT command is appended with
      completion_irq and entry is made in its_requests.
   4) On receiving completion_irq, vITS structure and its_requests
info is parsed
       and Creader of vITS is upstated with [ Cwriter vITS ] stored
for this request
       and this request is removed from its_requests.

 I am adding one INT per command. This can be improved to add one INT
cmd for all
 the pending commands. Existing Linux driver sends 2 commands at a time.

Regards
Vijay

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