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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 B9E78C37120 for ; Mon, 21 Jan 2019 21:29:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 75B9220861 for ; Mon, 21 Jan 2019 21:29:53 +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="SyFvu6eT" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727785AbfAUV3v (ORCPT ); Mon, 21 Jan 2019 16:29:51 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:55128 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727422AbfAUV3v (ORCPT ); Mon, 21 Jan 2019 16:29:51 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=9iIaPQrmUoxImEoqMmApMU/TQ6QplGJaZRBlEZeaw1w=; b=SyFvu6eTFI7hrB2JROBDfean3 /qfWXZFG/pQJrOObQr8Mf4HsLPMOqO26YjxB0kjWE+Nw4u2EwC/oqZU7HvtLjcNmXVFsGSqu70c2q HGDDdLAORY80a5uz9TimVUYwWtkyU4hoBRG0SI9J0DiC78p1P49KZMZvLGix7BcDwYoNQhxQR+2qP Q9oGTGwXbNiFSJIAoGjrvclcGkrODPIObiBKgy40Fgr3nBhKXGd1rVooJNtfG/hLcawW+911JcVWV dBHxFJxKEtKP3DsZNEe5r94uGKGFL1fF5XiBPhz28dy1pJR+gYa9yt359BIV/dd3twYqZEnrsmJU8 cLw4yoyDA==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1glh8d-0007Si-I2; Mon, 21 Jan 2019 21:29:47 +0000 Date: Mon, 21 Jan 2019 13:29:47 -0800 From: Christoph Hellwig To: Liam Mark Cc: Christoph Hellwig , Laura Abbott , sumit.semwal@linaro.org, arve@android.com, tkjos@android.com, maco@android.com, joel@joelfernandes.org, christian@brauner.io, devel@driverdev.osuosl.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, afd@ti.com, john.stultz@linaro.org Subject: Re: [PATCH 3/4] dma-buf: add support for mapping with dma mapping attributes Message-ID: <20190121212947.GA28620@infradead.org> References: <1547836667-13695-1-git-send-email-lmark@codeaurora.org> <1547836667-13695-4-git-send-email-lmark@codeaurora.org> <20190119102527.GA17723@infradead.org> <7ae73c39-9049-bcf6-775f-b0817ba0ec5f@redhat.com> <20190121083046.GD12420@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.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 Mon, Jan 21, 2019 at 11:44:10AM -0800, Liam Mark wrote: > The main use case is for allowing clients to pass in > DMA_ATTR_SKIP_CPU_SYNC in order to skip the default cache maintenance > which happens in dma_buf_map_attachment and dma_buf_unmap_attachment. In > ION the buffers aren't usually accessed from the CPU so this allows > clients to often avoid doing unnecessary cache maintenance. This can't work. The cpu can still easily speculate into this area. Moreover in general these operations should be cheap if the addresses aren't cached.