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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,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 2083FC433E1 for ; Tue, 18 Aug 2020 16:10:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F4147207DE for ; Tue, 18 Aug 2020 16:10:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="RpSSmTL8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728125AbgHRQKV (ORCPT ); Tue, 18 Aug 2020 12:10:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39640 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726974AbgHRQKN (ORCPT ); Tue, 18 Aug 2020 12:10:13 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 863BEC061342 for ; Tue, 18 Aug 2020 09:10:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Sks+YpGBOU4o5+prB+fPm+RZPeb7HCcfoore0HyIIVs=; b=RpSSmTL8+Q0fUzX/6x0fZWIQbm pWkqNSJ6xdJBXm3nP8g2FJMORjV6RY3nqtJtW96uGFjUFZfQzDU5yWqLPiimOvCCO1kvjzjvzo7q8 +JdxSb68PAC6angpC83DmKTvd6/tqe59v3IDDcp38+8NEpV8mAoC/Fr+PiAintL13vLfNz+Crthqo IlKLfGg2KJ7GcFqbBd4N9z1s0TtCRIvhoDagGX4oJdgmhvIDKIuvc0hFry98jKeDb1k2VzC7WA0e6 hiIsKy7aXvrHO8Lo8GWISkb6KSGOlslI8W6tAT/m9/C7LV/JYUYQVOaWA84ZWSPCsOoS/5FoB6Fqm DXjJYsUA==; Received: from hch by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1k84Bb-0006lM-1W; Tue, 18 Aug 2020 16:10:07 +0000 Date: Tue, 18 Aug 2020 17:10:06 +0100 From: Christoph Hellwig To: Will Deacon Cc: Cho KyongHo , janghyuck.kim@samsung.com, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, hyesoo.yu@samsung.com, iommu@lists.linux-foundation.org, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 1/2] dma-mapping: introduce relaxed version of dma sync Message-ID: <20200818161006.GA25124@infradead.org> References: <1597736591-20457-1-git-send-email-pullip.cho@samsung.com> <20200818082852.GA15145@willie-the-truck> <20200818093739.GB191752@KEI> <20200818100756.GA15543@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200818100756.GA15543@willie-the-truck> X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 18, 2020 at 11:07:57AM +0100, Will Deacon wrote: > > > so I'm not sure > > > that we should be complicating the implementation like this to try to > > > make it "fast". > > > > > I agree that this patch makes the implementation of dma API a bit more > > but I don't think this does not impact its complication seriously. > > It's death by a thousand cuts; this patch further fragments the architecture > backends and leads to arm64-specific behaviour which consequently won't get > well tested by anybody else. Now, it might be worth it, but there's not > enough information here to make that call. So it turns out I misread the series (*cough*, crazy long lines, *cough*), and it does not actually expose a new API as I thought, but it still makes a total mess of the internal interface. It turns out that on the for cpu side we already have arch_sync_dma_for_cpu_all, which should do all that is needed. We could do the equivalent for the to device side, but only IFF there really is a major benefit for something that actually is mainstream and matters.