Re: [PATCH v3 1/3] IRQ/Gic-V3: Add mbigen driver to support mbigen interrupt controller

[Marc Zyngier <marc.zyngier@arm.com>]

On 16/07/15 13:26, majun (F) wrote:
> 
> 
> 在 2015/7/16 17:30, Marc Zyngier 写道:
>> On 16/07/15 10:22, majun (F) wrote:
>>>
>>>
>>> 在 2015/7/16 16:52, Marc Zyngier 写道:
>>>> On 16/07/15 09:35, majun (F) wrote:
>>>
>>>>>> I'm a bit puzzled.
>>>>>
>>>>> For interrupts connect to mbigen , the interrupt trigger type, device id and
>>>>> event id value are encoded in mbigen chip already.
>>>>>
>>>>> There are two types of mbigen node within a mbigen chip.
>>>>> Type1: event id valud can't be programmed.
>>>>> Type2: event id value can be programmed.
>>>>>
>>>>> For example: An device with 5 interrupts connected to Mbigen node
>>>>> type 1.The default event id vlaue encoded in mbigen chip for these 5 interrupt
>>>>> is from 0 to 4.
>>>>>
>>>>> Because the event id value can't be programmed, we need to define all of
>>>>> 5 interrupts in dts file so that these 5 interrupt has
>>>>
>>>> You can define what you want in the device tree, the ITS doesn't care!
>>>> Nothing in the ITS code parses this property, and there is absolutely
>>>> zero chance that the even the ITS has allocated will actually match what
>>>> you expect.
>>>>
>>>> The ITS *relies* on the principle that the evenID can be programmed,
>>>> just like any MSI controller relies on the device to be programmed with
>>>> whatever payload has been provided. If all of a sudden we have to
>>>> support HW that has its own view of the payload, what you have here will
>>>> simply not work.
>>>>
>>> "If all of a sudden we have to
>>>  support HW that has its own view of the payload, what you have here will
>>>  simply not work."
>>>
>>> I am not very unstand this case, would you please explain this more detail?
>>
>> It is the ITS driver that allocates the eventID, not the device. If your
>> hardware has decided that it will use event 5, while the ITS expect it
>> to use event 3, nothing will work. And there is no way for the ITS to
>> know which event your device is using (it doesn't parse your device's
>> device tree).
>>
> Yes, I agree with you that eventID should be allocated by ITS driver.
> But I want to explain the case you said above can be avoided.
> 
> For example, An device with total 5 interrupts connected to Mbigen node.
> In mbigen chip, the default eventID value for each device starts from 0.
> So, for these 5 interrupts the default eventID value is from 0 to 4.
> 
> Because the default eventID is fixed in mbigen chip, to make these 5 interrupt
> work, the only way is define all these 5 interrupts in dts file.

But the ITS doesn't read these interrupts, and won't let you program the
translation either.

> When irq initializing, ITS driver will allocat LPI interrupt number for these
> 5 interrupts, for example : from 8192 to 8196. and the eventID value is from 0 to 4.
> Now, the allocated eventID value same as the eventID value encoded in mbigen chip,
> The interrupt can work.

But that's pure luck! What if I decide to change the allocation method
so that all the devices share a common ITT?

Have you really hardcoded the Linux behaviour in your hardware?

> I know this is not a good method,but for current mbigen chip,it's the only solution.

I'm sorry, I can't call this a solution.

	M.
-- 
Jazz is not dead. It just smells funny...