Re: [PATCH v7 18/28] xen/arm: ITS: Export ITS info to Virtual ITS

[Julien Grall <julien.grall@citrix.com>]

Hi Ian,

On 24/09/15 09:27, Ian Campbell wrote:
> On Thu, 2015-09-24 at 10:56 +0530, Vijay Kilari wrote:
> 
>>>> +
>>>>          plpi = its_get_plpi(pdev, i);
>>>>          /* TODO: Route lpi */
>>>>      }
>>>> @@ -1366,6 +1374,8 @@ static int its_probe(struct dt_device_node
>>>> *node)
>>>>      its->phys_size = its_size;
>>>>      typer = readl_relaxed(its_base + GITS_TYPER);
>>>>      its->ite_size = ((typer >> 4) & 0xf) + 1;
>>>> +    its_data.eventID_bits = GITS_TYPER_IDBITS(typer);
>>>> +    its_data.devID_bits = GITS_TYPER_DEVBITS(typer);
>>>
>>> The 2 fields will be override every time a new ITS node will be
>>> initialized.
>>>
>>> What ensure that all the ITS have the same number of Event ID and
>>> Device ID?
>>
>> Nothing of I thing of ensures this at HW level.
> 
> The question here is about the behaviour of the software emulation.
> 
>>  Either we should
>> assume that all the ITS
>> have number of Event and Device ID or we choose lower of all the ITS?.
> 
> Don't we need, if anything, the highest?

It's worth mentioning that there is no generic mechanism to notify if a
command is invalid. So passing an out of range DevID and EventID in a
command may potentially result to crashing Xen because we receive an SError.

So we can use the highest value only if we have all the safety in Xen to
prevent to send any command invalid out of range value.

Regards,

-- 
Julien Grall