From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: [PATCH] ARM: DT: Add binding for GIC virtualization extentions (VGIC) Date: Thu, 05 Apr 2012 15:07:22 +0100 Message-ID: <4F7DA71A.4020809@arm.com> References: <1333384217-13441-1-git-send-email-marc.zyngier@arm.com> <4F7AC138.9020308@citrix.com> <4F7AC8A8.9020606@arm.com> <20120403153538.0D1B83E044A@localhost> <4F7D974C.9050506@arm.com> <4F7D9F5A.9030709@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4F7D9F5A.9030709@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-arm-kernel-bounces@lists.infradead.org Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Rob Herring Cc: Grant Likely , "devicetree-discuss@lists.ozlabs.org" , "rob.herring@calxeda.com" , David Vrabel , "linux-arm-kernel@lists.infradead.org" List-Id: devicetree@vger.kernel.org On 05/04/12 14:34, Rob Herring wrote: > On 04/05/2012 07:59 AM, Marc Zyngier wrote: >> On 03/04/12 16:35, Grant Likely wrote: >> >> Hi Grant, >> >>> On Tue, 03 Apr 2012 10:53:44 +0100, Marc Zyngier wrote: >>>> On 03/04/12 10:22, David Vrabel wrote: >>>> >>>> Hi David, >>>> >>>>> On 02/04/12 17:30, Marc Zyngier wrote: >>>>>> The GICv2 can have virtualization extension support, consisting >>>>>> of an additional set of registers and interrupts. Add the necessary >>>>>> binding to the GIC DT documentation. >>>>> >>>>> The Xen hypervisor's device tree support is very much incomplete so I've >>>>> not looked into this is much detail. >>>>> >>>>> Would it make more sense to extend the existing gic binding with the the >>>>> additional information rather than adding a new node? >>>> >>>> I'm actually torn between the two approaches. On one side, the VGIC is >>>> part of the GIC spec, hence should be part of the GIC node. On the other >>>> hand, it is logically handled by a different piece of software (the >>>> hypervisor), and would normally be probed separately. Having a separate >>>> node makes the probing more sensible. >>> >>> Don't get too hung up on the software side of things. Describe it in >>> a way that makes sense for the hardware. There is lots of precidence >>> for two hunks of software initializating from the same node; either by >>> probe kicking off two init hooks, or by early init code going looking >>> for the node manually. >> >> What I'm trying to avoid is a royal mess in the future if we get some >> other extension to the GIC. >> > > But that would be a new compatible string as is this case. Yes, probably. >> Let's say we implement the following: >> >> gic: interrupt-controller@2c001000 { >> compatible = "arm,cortex-a15-gic"; >> #interrupt-cells = <3>; >> #address-cells = <1>; >> interrupt-controller; >> reg = <0x2c001000 0x1000>, >> <0x2c002000 0x100>, >> <0x2c004000 0x2000>, >> <0x2c006000 0x2000>; >> interrupts = <1 9 0xf04>; > > Does this work having an interrupt within the parent itself? Normally > this would be the connection to the next level up. In this case we don't have an interrupt parent property, so the GIC is properly identified as the top-level interrupt controller. This is admittedly a bit fragile, and contradicts the current wording of the binding. >> }; >> >> It's all fine (the two last regions and the interrupt are for VGIC), >> until someone comes up with extension FOO which requires two new regions >> and am interrupt. It is then impossible to distinguish between the two, >> short of adding more attributes. >> >> How about this? >> >> gic: interrupt-controller@2c001000 { >> compatible = "arm,cortex-a15-gic"; >> #interrupt-cells = <3>; >> #address-cells = <1>; >> #size-cells = <1>; >> interrupt-controller; >> reg = <0x2c001000 0x1000>, >> <0x2c002000 0x100>; >> >> vgic@2c004000 { >> compatible = "arm,cortex-a15-vgic", "arm,vgic"; >> reg = <0x2c004000 0x2000>, >> <0x2c006000 0x2000>; >> interrupts = <1 9 0xf04>; >> }; >> }; >> >> It cleanly separate the extension from the core GIC, and still make it >> part of the GIC node. >> >> What do you think? >> > > I prefer the first option. The first I posted (vgic node outside of the gic), or the one with everything in the same node? M. -- Jazz is not dead. It just smells funny...