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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=ham 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 4C94FC433E6 for ; Mon, 22 Feb 2021 12:07:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0A8D464E44 for ; Mon, 22 Feb 2021 12:07:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230202AbhBVMHh (ORCPT ); Mon, 22 Feb 2021 07:07:37 -0500 Received: from foss.arm.com ([217.140.110.172]:43906 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229780AbhBVMHE (ORCPT ); Mon, 22 Feb 2021 07:07:04 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B89751FB; Mon, 22 Feb 2021 04:06:18 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.51.127]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DBB993F70D; Mon, 22 Feb 2021 04:06:16 -0800 (PST) Date: Mon, 22 Feb 2021 12:06:14 +0000 From: Mark Rutland To: Marc Zyngier Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, james.morse@arm.com, marcan@marcan.st, tglx@linutronix.de, will@kernel.org Subject: Re: [PATCH 5/8] arm64: irq: add a default handle_irq panic function Message-ID: <20210222120614.GC70951@C02TD0UTHF1T.local> References: <20210219113904.41736-1-mark.rutland@arm.com> <20210219113904.41736-6-mark.rutland@arm.com> <20210222095913.GA70951@C02TD0UTHF1T.local> <1d2c27d72b9b2cbdb83d25165a20559a@kernel.org> <20210222112544.GB70951@C02TD0UTHF1T.local> <2e6a9659eabcccb355318ff7214c8d1f@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2e6a9659eabcccb355318ff7214c8d1f@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 22, 2021 at 11:43:13AM +0000, Marc Zyngier wrote: > On 2021-02-22 11:25, Mark Rutland wrote: > > On Mon, Feb 22, 2021 at 10:48:11AM +0000, Marc Zyngier wrote: > > > On 2021-02-22 09:59, Mark Rutland wrote: > > > > On Fri, Feb 19, 2021 at 11:39:01AM +0000, Mark Rutland wrote: > > > > > +void (*handle_arch_irq)(struct pt_regs *) __ro_after_init = > > > > > default_handle_irq; > > > > > > > > > > int __init set_handle_irq(void (*handle_irq)(struct pt_regs *)) > > > > > { > > > > > - if (handle_arch_irq) > > > > > + if (handle_arch_irq != default_handle_irq) > > > > > return -EBUSY; > > > > > > > > > > handle_arch_irq = handle_irq; > > > > > @@ -87,7 +92,7 @@ void __init init_IRQ(void) > > > > > init_irq_stacks(); > > > > > init_irq_scs(); > > > > > irqchip_init(); > > > > > - if (!handle_arch_irq) > > > > > + if (handle_arch_irq == default_handle_irq) > > > > > panic("No interrupt controller found."); > > > > > > It also seems odd to have both default_handle_irq() that panics, > > > and init_IRQ that panics as well. Not a big deal, but maybe > > > we should just drop this altogether and get the firework on the > > > first interrupt. > > > > My gut feeling was that both were useful, and served slightly different > > cases: > > > > * The panic in default_handle_irq() helps if we unexpectedly unmask IRQ > > too early. This is mostly a nicety over the current behaviour of > > branching to NULL in this case. > > > > * The panic in init_IRQ() gives us a consistent point at which we can > > note the absence of a root IRQ controller even if all IRQs are > > quiescent. This is a bit nicer to debug than seeing a load of driver > > probes fail their request_irq() or whatever. > > > > ... so I'd err on the side of keeping both, but if you think otherwise > > I'm happy to change this. > > As I said, it's not a big deal. I doubt that we'll see default_handle_irq() > exploding in practice. But the real nit here is the difference of treatment > between IRQ and FIQ. *IF* we ever get a system that only signals its > interrupt as FIQ (and I don't see why we'd forbid that), then we would That's a fair point. For consistency, we could remove the init_IRQ() panic() and instead log the registered handlers, e.g. | pr_info("Root IRQ handler is %ps\n", handle_arch_irq); | pr_info("Root FIQ handler is %ps\n", handle_arch_fiq); ... or do that inside the set_handle_{irq,fiq}() functions. That way the messages (or absence thereof) would be sufficient to diagnose the lack of a root IRQ/FIQ handler when IRQ/FIQ happens to be quiescent. Does that sound any better? > To be clear, I don't think we should care too much either way, and I'm > fine with the code as is. Sure, and FWIW I agree with the nit! Thanks, Mark.