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

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Date:	Thu, 16 Jul 2015 10:30:01 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	"majun (F)" <majun258@...wei.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Will Deacon <Will.Deacon@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"lizefan@...wei.com" <lizefan@...wei.com>,
	"huxinwei@...wei.com" <huxinwei@...wei.com>,
	"dingtianhong@...wei.com" <dingtianhong@...wei.com>,
	"zhaojunhua@...ilicon.com" <zhaojunhua@...ilicon.com>,
	"liguozhu@...ilicon.com" <liguozhu@...ilicon.com>,
	"xuwei5@...ilicon.com" <xuwei5@...ilicon.com>,
	"wei.chenwei@...ilicon.com" <wei.chenwei@...ilicon.com>,
	"guohanjun@...wei.com" <guohanjun@...wei.com>,
	"wuyun.wu@...wei.com" <wuyun.wu@...wei.com>,
	"guodong.xu@...aro.org" <guodong.xu@...aro.org>,
	"haojian.zhuang@...aro.org" <haojian.zhuang@...aro.org>,
	"zhangfei.gao@...aro.org" <zhangfei.gao@...aro.org>,
	"usman.ahmad@...aro.org" <usman.ahmad@...aro.org>
Subject: Re: [PATCH v3 1/3] IRQ/Gic-V3: Add mbigen driver to support mbigen
 interrupt controller

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).

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