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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 C6572C07E95 for ; Fri, 16 Jul 2021 15:35:01 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 8CFBA60238 for ; Fri, 16 Jul 2021 15:35:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8CFBA60238 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com 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=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:Cc:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=buPiB3NsRC10L/1goQ25V6vLc+By6gVVOlo3sr7C1FI=; b=H5N4+IWUE1Er/Cv0+HNsFd8uM9 aVWaR6yZI1NIiY+Qfs6pkqqPE3NhoKMmRBhUjsn4kjTGAXvxkblD5/QNl5vGiYmYE+WB2aWGGCIUw AceW/3mFgKFlcruwdfwtKoiW/HzStg8Mgk+iSPFDhz1h6urhArfK2N9DeyngCjrXXP8aQS8r5qeUx NiiqRiJkKlc/HUpwSeyi0WKrk2oC+qKWOx+6ZJHu3DxsIh3Jh/h3rYMsnSRPVt3bkQi2JNrRtvQSF frPoRpZb/gzgWO0pOugZ8kNA5ZO64GPCOzhy7IVZvDcqImRbZCF976j22CKA6Y1SXikNk51oXyJro mE/A1+OQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1m4Ppr-004j4Q-KO; Fri, 16 Jul 2021 15:33:07 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1m4Ppm-004j36-Iy for linux-arm-kernel@lists.infradead.org; Fri, 16 Jul 2021 15:33:04 +0000 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 74B81D6E; Fri, 16 Jul 2021 08:32:59 -0700 (PDT) Received: from [10.57.36.240] (unknown [10.57.36.240]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A607E3F774; Fri, 16 Jul 2021 08:32:56 -0700 (PDT) Subject: Re: [PATCH v4 0/3] Apple M1 DART IOMMU driver To: Christoph Hellwig Cc: Sven Peter , Will Deacon , Joerg Roedel , Arnd Bergmann , devicetree@vger.kernel.org, Hector Martin , linux-kernel@vger.kernel.org, Marc Zyngier , Mohamed Mediouni , Stan Skowronek , linux-arm-kernel@lists.infradead.org, Mark Kettenis , iommu@lists.linux-foundation.org, Alexander Graf , Alyssa Rosenzweig , Rob Herring , r.czerwinski@pengutronix.de, Mauro Carvalho Chehab , linux-media@vger.kernel.org References: <20210627143405.77298-1-sven@svenpeter.dev> <7261df01-34a9-4e53-37cd-ae1aa15b1fb4@arm.com> From: Robin Murphy Message-ID: <0d20bd6b-d0a1-019c-6398-b12f83f4fdf7@arm.com> Date: Fri, 16 Jul 2021 16:32:50 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210716_083302_735396_DE852E63 X-CRM114-Status: GOOD ( 13.44 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 2021-07-16 07:24, Christoph Hellwig wrote: > On Wed, Jul 14, 2021 at 07:19:50PM +0100, Robin Murphy wrote: >> Even at the DMA API level you could hide *some* of it (at the cost of >> effectively only having 1/4 of the usable address space), but there are >> still cases like where v4l2 has a hard requirement that a page-aligned >> scatterlist can be mapped into a contiguous region of DMA addresses. > > Where does v4l2 make that broken assumption? Plenty of dma mapping > implementations including dma-direct do not support that. See vb2_dc_get_contiguous_size() and its callers. I still remember spending an entire work day on writing one email at the culmination of this discussion: https://lore.kernel.org/linux-iommu/56409B6D.5090903@arm.com/ 809eac54cdd6 was framed as an efficiency improvement because it technically was one (and something I had wanted to implement anyway), but it was also very much to save myself from any further email debates or customer calls about "regressing" code ported from 32-bit platforms... Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel