Re: [Xen-devel] [PATCH for-4.5 7/8] xen/irq: Handle multiple action per IRQ

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hello Jan,

On 02/24/2014 02:48 PM, Julien Grall wrote:
> On 02/24/2014 02:32 PM, Jan Beulich wrote:
>>>>> On 24.02.14 at 15:08, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
>>> (Adding Jan for x86 part).
>>>
>>> On 02/20/2014 09:29 PM, Julien Grall wrote:
>>>> Hi Ian,
>>>>
>>>> On 02/19/2014 11:55 AM, Ian Campbell wrote:
>>>>> On Fri, 2014-01-24 at 16:43 +0000, Julien Grall wrote:
>>>>>> On ARM, it may happen (eg ARM SMMU) to setup multiple handler for the 
>>>>>> same
>>>>>> interrupt.
>>>>>
>>>>> Mention here that you are therefore creating a linked list of actions
>>>>> for each interrupt.
>>>>>
>>>>> If you use xen/list.h for this then you get a load of helpers and
>>>>> iterators which would save you open coding them.
>>>>
>>>> After thinking, using xen/list.h won't really remove open code, except
>>>> removing "action_ptr" in release_dt_irq.
>>>>
>>>> Calling release_dt_irq to an IRQ with multiple action shouldn't be
>>>> called often. Therefore, having both prev and next is a waste of space.
>>>
>>> Jan, as it's common code, do you have any thoughts?
>>
>> In fact I'm not convinced this action chaining is correct in the first
>> place, as mentioned by Ian too (considering the potential sharing
>> between hypervisor and guest). Furthermore, if this is really just
>> about IOMMU handlers, why can't the SMMU code register a single
>> action and disambiguate by the dev_id argument passed to the
>> handler?
> 
> The patch #3 of this serie protects the IRQ to be shared with the domain.
> 
> I should have remove "eg ARM SMMU" in the description. ARM SMMU is not
> the only the case, we don't know in advance if the IRQ will be shared
> (except browsing the DT and checking if this IRQ was used by another
> devices...). We may have the same thing with other devices.
> 
> The logic is painful to handle internally in ARM SMMU driver while we
> can handle it generically. No need to duplicate the code when a new
> driver will have the same problem.
> 

I haven't heard any answer from you. Shall I take as a "go"?

Regards,

-- 
Julien Grall

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