From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: [PATCH v2] ARM: DT: Add binding for GIC virtualization extentions (VGIC) Date: Wed, 09 May 2012 22:42:05 +0200 Message-ID: <37e096905f891fc6abdccf8977bd7447@localhost> References: <1336586277-28454-1-git-send-email-marc.zyngier@arm.com> <201205091921.43299.arnd@arndb.de> <201205092027.50059.arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <201205092027.50059.arnd-r2nGTMty4D4@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Sender: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org To: Arnd Bergmann Cc: devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, david.vrabel-Sxgqhf6Nn4DQT0dZR+AlfA@public.gmane.org, rob.herring-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: devicetree@vger.kernel.org On Wed, 9 May 2012 20:27:49 +0000, Arnd Bergmann wrote: > On Wednesday 09 May 2012, Marc Zyngier wrote: >> On Wed, 9 May 2012 19:21:42 +0000, Arnd Bergmann wrote: >> > On Wednesday 09 May 2012, 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. >> >> >> >> Signed-off-by: Marc Zyngier >> > >> > Would it make sense to add a way to detect whether a GIC is virtual >> > or real? Maybe an optional empty "virtual-gic" property or an >> > additional >> > "compatible" value. Even if we don't need it now, it might come in >> > handy >> > if we require it already. >> >> I don't really see a need for this. When running on a virtual machine, >> the >> kernel cannot tell if this is the real thing or not (the virtual CPU >> interface looks exactly like the normal one once mapped into the guest >> address space). >> >> Or maybe I just didn't get your use case? > > Well, one difference seems to be the VGIC maintainance interrupt that may > or may not be present, and another one the additional registers. Of course > you can imply the type of GIC from the presence of this extra data, > but I think it would be better to make it explicit. Ah, I see what you mean. But these registers and interrupt are actually only visible on the hypervizor side. The guest shouldn't see any of this. I suppose we could have a "arm,has-virt-extensions" property in devices that implement the virtualization extensions (GIC, timers...). What do you think? M. -- Fast, cheap, reliable. Pick two.