Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756723AbaFYNTJ (ORCPT ); Wed, 25 Jun 2014 09:19:09 -0400 Received: from mail-vc0-f177.google.com ([209.85.220.177]:34567 "EHLO mail-vc0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754206AbaFYNTI (ORCPT ); Wed, 25 Jun 2014 09:19:08 -0400 MIME-Version: 1.0 In-Reply-To: <86oaxhjg4r.fsf@arm.com> References: <1403688530-23273-1-git-send-email-marc.zyngier@arm.com> <1403688530-23273-4-git-send-email-marc.zyngier@arm.com> <86oaxhjg4r.fsf@arm.com> From: Rob Herring Date: Wed, 25 Jun 2014 08:18:46 -0500 Message-ID: Subject: Re: [RFC PATCH 3/9] irqchip: GIC: Convert to EOImode == 1 To: Marc Zyngier Cc: "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Catalin Marinas , Thomas Gleixner , Will Deacon , Christoffer Dall , "eric.auger@linaro.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 25, 2014 at 8:03 AM, Marc Zyngier wrote: > On Wed, Jun 25 2014 at 01:50:12 PM, Rob Herring wrote: >> On Wed, Jun 25, 2014 at 4:28 AM, Marc Zyngier wrote: >>> So far, GICv2 has been used in with EOImode == 0. The effect of this >>> mode is to perform the priority drop and the deactivation of the >>> interrupt at the same time. >>> >>> While this works perfectly for Linux (we only have a single priority), >>> it causes issues when an interrupt is forwarded to a guest, and when >>> we want the guest to perform the EOI itself. >>> >>> For this case, the GIC architecture provides EOImode == 1, where: >>> - A write to the EOI register drops the priority of the interrupt and leaves >>> it active. Other interrupts at the same priority level can now be taken, >>> but the active interrupt cannot be taken again >>> - A write to the DIR marks the interrupt as inactive, meaning it can >>> now be taken again. >>> >>> We only enable this feature when booted in HYP mode. Also, as most device >>> trees are broken (they report the CPU interface size to be 4kB, while >>> the GICv2 CPU interface size is 8kB), output a warning if we're booted >>> in HYP mode, and disable the feature. >> >> Why not fix-up the size so the feature can be enabled? > > Is it a bet we're willing to take? We'd end-up with a kernel that > doesn't boot if the DT was actually right. If we stay with EOImode==0, > we can still boot (KVM will probably be broken though). I think so. Seems like your last statement answers this. Why is KVM not working on my system seems like a much more likely and frequent support issue than a potentially broken system. The only place I really could see it be broken is an SBSA system doing the address swizzling trick with the gic-400 to get 64KB spaced regions but does not use the 60KB aligned cpu interface address. But DTBs are hardly stable for 64-bit systems and can be updated. Rob -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/