linux-kernel - Re: [PATCH 4/4 V3] irqchip: gicv2m: Add support for multiple MSI for ARM64 GICv2m

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Date:	Fri, 1 Aug 2014 11:19:18 -0500
From:	Suravee Suthikulanit <suravee.suthikulpanit@....com>
To:	Marc Zyngier <marc.zyngier@....com>
CC:	Mark Rutland <Mark.Rutland@....com>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	Pawel Moll <Pawel.Moll@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Harish.Kasiviswanathan@....com" <Harish.Kasiviswanathan@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 4/4 V3] irqchip: gicv2m: Add support for multiple MSI
 for ARM64 GICv2m

On 8/1/2014 9:51 AM, Marc Zyngier wrote:
> Hi Suravee,
>
> On 01/08/14 15:36, Suravee Suthikulanit wrote:
>> On 7/30/2014 10:16 AM, Marc Zyngier wrote:
>>> Why do we need this complexity at all? Is there any case where we'd want
>>> to limit ourselves to a single vector for MSI?
>>
>> I think the ARM64 GICv2m should not be the limitation for the devices
>> multiple MSI if there is no real hardware/design limitation.
>>
>>> arm64 is a new enough architecture so that we can expect all interrupt controllers to cope
>>> with that.
>>
>> I am not sure if I understand this comment.
>>
>> We are not forcing all interrupt controllers for ARM64 to handle
>> multi-MSI.  They have the option to support if multi-MSI if they want
>> to. I just think that we should not put the architectural limit here.
>
> Let me be clearer: I think we should put the burden of *not* handling
> multi-MSI on interrupt controllers. Here, you're making the
> architectural default to be "I don't support multi-MSI", hence having to
> override global vectors and such for well behaved MSI controllers like
> GICv2m and GICv3 ITS.
>
> Let's only support multi-MSI for the time being. If someone comes up
> with a silly old MSI controller that can't deal with it, we'll address
> the issue at that problem.
>
> Thanks,
>
> 	M.
>

Ok, I'm fine with that. Thanks for clarification.

Suravee

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