From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35D87C2B9F4 for ; Tue, 22 Jun 2021 17:32:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1BD7861107 for ; Tue, 22 Jun 2021 17:32:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231991AbhFVRfG (ORCPT ); Tue, 22 Jun 2021 13:35:06 -0400 Received: from mail.kernel.org ([198.145.29.99]:43476 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229501AbhFVRfF (ORCPT ); Tue, 22 Jun 2021 13:35:05 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F2CDD61075; Tue, 22 Jun 2021 17:32:49 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1lvkGV-009E0J-Re; Tue, 22 Jun 2021 18:32:48 +0100 Date: Tue, 22 Jun 2021 18:32:47 +0100 Message-ID: <87sg19by9s.wl-maz@kernel.org> From: Marc Zyngier To: Boqun Feng Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, Arnd Bergmann , Bjorn Helgaas , Linux ARM , Catalin Marinas , Will Deacon Subject: Re: [RFC 0/2] irqchip/gic-v3-its: Introduce virtual ITS In-Reply-To: <20210622155313.3819952-1-boqun.feng@gmail.com> References: <20210622155313.3819952-1-boqun.feng@gmail.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: boqun.feng@gmail.com, tglx@linutronix.de, linux-kernel@vger.kernel.org, arnd@arndb.de, bhelgaas@google.com, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 22 Jun 2021 16:53:11 +0100, Boqun Feng wrote: > > Hi Marc, > > Here is an RFC for supporting platforms having LPI supported but without > ITS. And this is for the virtual PCI support for ARM64 Hyper-V guests. > We currently choose this approach (LPI w/o ITS) because a) it's allowed > for GICv3 and b) ITS may not be a more efficient way to configure LPIs > compared to hypercalls, but we'd like to get feedbacks from the > community. > > Besides, patch #1 fixes a bug which I found while I was at it. > > Looking forwards to any comment and suggestion! My suggestion is to not do that. The ITS driver is used to drive an ITS. That, and only that. The simple fact that you mention hypercalls shows that this is *not* what the architecture allows. So if you are going to implement something that is evidently outside of the scope of the architecture, keep it in some Hyper-V specific code that doesn't involve the ITS driver. All you need is something that will piggy-back on top of the GIC driver using a hierarchical driver. We support that today. Of course, you'll have to invent your own firmware interface for discovery. Thanks, M. -- Without deviation from the norm, progress is not possible.