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=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 D6451C433E0 for ; Mon, 8 Feb 2021 15:32:47 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6CFFA64DFF for ; Mon, 8 Feb 2021 15:32:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6CFFA64DFF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=marcan.st Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:Subject: From:References:To:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=hUvmk3GAVQLu6fTEAzBJj+2eLwSn47nurDT78/vQBDE=; b=rkgq+GSpkdDS/KF4tN/SNrLZd SYd059i7f2NH43QPdbzAA9FfiJMeOtPQDewcwFnRU5dUQyCuHWiAI/rkwKLMwTn13Le5neYPgeaVF PSv3dAdrYdA9OXjl2w0LqvRgsYnxt6WkKrlzTRG3NhJMAAaODH74c7ABSL3Sj0zStNRdThFYDtx3E iyaV+EzV/d0dZsy5MPLp9YkEsB2TokNKHpi9e1DCKW1LpLpr4zUSoSQrjiH/PFWYb3Oh4sevORySz SolxZzGf6bnIacBDj3q9pTvMTa09P/o4ODU089Eo0+QgL3mceZ1gLI4l5COIH/LFaqyUU4tcq26me OpsnQtU9w==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l98Vd-0002Xe-Us; Mon, 08 Feb 2021 15:31:30 +0000 Received: from marcansoft.com ([212.63.210.85] helo=mail.marcansoft.com) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1l98Va-0002Wt-Lc for linux-arm-kernel@lists.infradead.org; Mon, 08 Feb 2021 15:31:27 +0000 Received: from [127.0.0.1] (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) (Authenticated sender: marcan@marcan.st) by mail.marcansoft.com (Postfix) with ESMTPSA id D408541F47; Mon, 8 Feb 2021 15:31:20 +0000 (UTC) To: Marc Zyngier , Arnd Bergmann References: <20210204203951.52105-1-marcan@marcan.st> <20210204203951.52105-16-marcan@marcan.st> <87eehqlxlr.wl-maz@kernel.org> <87a6selrkt.wl-maz@kernel.org> From: Hector Martin Subject: Re: [PATCH 15/18] irqchip/apple-aic: Add support for the Apple Interrupt Controller Message-ID: Date: Tue, 9 Feb 2021 00:31:18 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <87a6selrkt.wl-maz@kernel.org> Content-Language: es-ES X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210208_103126_826172_01B266AD X-CRM114-Status: GOOD ( 19.41 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Cc: DTML , "linux-kernel@vger.kernel.org" , SoC Team , Rob Herring , Olof Johansson , Linux ARM Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 08/02/2021 20.36, Marc Zyngier wrote: > On Mon, 08 Feb 2021 10:29:23 +0000, > Arnd Bergmann wrote: >> >> On Mon, Feb 8, 2021 at 10:25 AM Marc Zyngier wrote: >>> On Thu, 04 Feb 2021 20:39:48 +0000, Hector Martin wrote: >> >>>> +{ >>>> + return readl(ic->base + reg); >>> >>> Please consider using the _relaxed accessors, as I don't think any of >>> these interacts with memory (apart from IPIs, of course). >> >> MSI interrupts require serializing with DMA, so at the minimum I think there >> needs to be something that ensures that DMA from device into memory >> has completed before delivering the completion interrupt to a driver. This >> may already be implied when the AIC is entered, but this is hard to know >> without actual hardware specs. > > If there is a sync with memory required, it should happen at the point > where it is Acked, not when masked/unmasked or anything else. And > given that you want to sync with an external agent (the DMA producer), > the DMB generated by readl won't save you, as it only orders CPU > accesses AFAICT. Found an doc that talks about this, but then... how does the current Linux code work anyway for normal use cases? https://elinux.org/images/7/73/Deacon-weak-to-weedy.pdf That says dmb is not enough for DMA-control to DMA-data dependencies due to speculation, which is what we have here and the situation I described (with an IRQ along the way, but that's irrelevant). But that's what readl does: a read followed by a dmb(oshld) followed by a control dependency (but that needs an isb to take effect). How does this not break drivers that read DMA-accessed memory after a readl of a status register? I thought that was the point of the non-relaxed functions. -- Hector Martin (marcan@marcan.st) Public Key: https://mrcn.st/pub _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel