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

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Message-ID: <53DBA986.90705@arm.com>
Date:	Fri, 01 Aug 2014 15:51:50 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Suravee Suthikulanit <suravee.suthikulpanit@....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

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