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=-9.0 required=3.0 tests=BAYES_00,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 F1E32C433DB for ; Mon, 22 Feb 2021 11:44:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9E5D164E27 for ; Mon, 22 Feb 2021 11:44:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230041AbhBVLoB (ORCPT ); Mon, 22 Feb 2021 06:44:01 -0500 Received: from mail.kernel.org ([198.145.29.99]:40388 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229947AbhBVLn7 (ORCPT ); Mon, 22 Feb 2021 06:43:59 -0500 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 B1F3764ED6; Mon, 22 Feb 2021 11:43:16 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1lE9cP-00FJBa-Ih; Mon, 22 Feb 2021 11:43:13 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Mon, 22 Feb 2021 11:43:13 +0000 From: Marc Zyngier To: Mark Rutland 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 In-Reply-To: <20210222112544.GB70951@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> User-Agent: Roundcube Webmail/1.4.11 Message-ID: <2e6a9659eabcccb355318ff7214c8d1f@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: mark.rutland@arm.com, 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 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 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 To be clear, I don't think we should care too much either way, and I'm fine with the code as is. M. -- Jazz is not dead. It just smells funny...