linux-kernel - Re: [PATCH v2 2/3] IRQ/Gic-V3: Change arm-gic-its to support the Mbigen interrupt

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Message-ID: <558D110D.7050000@arm.com>
Date:	Fri, 26 Jun 2015 09:45:01 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	"majun (F)" <majun258@...wei.com>
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 <dingtianhong@...wei.com>,
	吴云 <wuyun.wu@...wei.com>,
	赵俊化 <zhaojunhua@...ilicon.com>,
	"liguozhu@...ilicon.com" <liguozhu@...ilicon.com>,
	许威 <xuwei5@...ilicon.com>,
	chenwei <wei.chenwei@...ilicon.com>
Subject: Re: [PATCH v2 2/3] IRQ/Gic-V3: Change arm-gic-its to support the
 Mbigen interrupt

On 23/06/15 10:29, Thomas Gleixner wrote:
> On Tue, 23 Jun 2015, majun (F) wrote:
>> 在 2015/6/19 7:52, Thomas Gleixner 写道:
>>> On Mon, 15 Jun 2015, majun (F) wrote:
>>>> 在 2015/6/12 18:48, Thomas Gleixner 写道:
>>>>> Can you please provide a proper description of this mbigen chip and
>>>>> explain WHY you think that it needs all this special hackery?
>>>
>>> You carefully avoided to provide a proper description of this mbigen
>>> chip and how it needs to be integrated into the GIC/ITS whatever
>>> scenario.
>>>
>> Mbigen means Message Based Interrupt Generator.
>> Its a kind of interrupt controller collects
>> the interrupts from external devices and generate msi interrupt.
>>
>> Mbigen is applied to reduce the number of wire connected interrupts.
>>
>> As the peripherals increasing, the interrupts lines needed is increasing
>> much, especially on the Arm64 server soc.
>>
>> Therefore, the interrupt pin in gic is not enought for so many perpherals.
>>
>> Mbigen is designed to fix this problem.
>>
>> Mbigen chip locates in ITS or outside of ITS.
>>
>> The working flow of Mbigen shows as below:
>>
>> external devices ------> MBIGEN ------->ITS
>>
>> The devices connect to Mbigen chip through wire connecting way.
>> Mbigen detects and collectes the interrupts from the these devices.
>>
>> Then, Mbigen generats the MBI interrupts by writting the ITS
>> Translator register.
> 
> So it's nothing else than a non PCI based MSI implementation which
> means it can simply use the generic MSI infrastructure and implement a
> interrupt domain/chip which implements the MBI specific parts and has
> the ITS as its parent domain.
> 
> No hackery in ITS and no extra functionality in the core irq code. It
> just can use the existing infrastructure. The only extra you need is a
> proper way to retrieve the pointer to the ITS domain. Everything else
> just falls in place.

I may have a proposal for that. Stay tuned.

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