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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 6F4BCC4CECE for ; Mon, 16 Mar 2020 12:47:03 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (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 27F83205ED for ; Mon, 16 Mar 2020 12:47:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 27F83205ED Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 25FD02156B; Mon, 16 Mar 2020 12:47:02 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id K4XjISN0bHO1; Mon, 16 Mar 2020 12:47:01 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id EDBA320774; Mon, 16 Mar 2020 12:47:00 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id E399BC18DA; Mon, 16 Mar 2020 12:47:00 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) by lists.linuxfoundation.org (Postfix) with ESMTP id 4E2E6C013E for ; Mon, 16 Mar 2020 12:46:59 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 3C4FD2152A for ; Mon, 16 Mar 2020 12:46:59 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id FynfLIbsaVj6 for ; Mon, 16 Mar 2020 12:46:57 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by silver.osuosl.org (Postfix) with ESMTPS id 31A3820774 for ; Mon, 16 Mar 2020 12:46:57 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 1711468CEC; Mon, 16 Mar 2020 13:46:53 +0100 (CET) Date: Mon, 16 Mar 2020 13:46:52 +0100 From: Christoph Hellwig To: Robin Murphy Subject: Re: [RFC][PATCH] dma-mapping: align default segment_boundary_mask with dma_mask Message-ID: <20200316124652.GA17386@lst.de> References: <20200314000007.13778-1-nicoleotsuka@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Cc: Nicolin Chen , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, hch@lst.de X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Mon, Mar 16, 2020 at 12:12:08PM +0000, Robin Murphy wrote: > On 2020-03-14 12:00 am, Nicolin Chen wrote: >> More and more drivers set dma_masks above DMA_BIT_MAKS(32) while >> only a handful of drivers call dma_set_seg_boundary(). This means >> that most drivers have a 4GB segmention boundary because DMA API >> returns DMA_BIT_MAKS(32) as a default value, though they might be >> able to handle things above 32-bit. > > Don't assume the boundary mask and the DMA mask are related. There do exist > devices which can DMA to a 64-bit address space in general, but due to > descriptor formats/hardware design/whatever still require any single > transfer not to cross some smaller boundary. XHCI is 64-bit yet requires > most things not to cross a 64KB boundary. EHCI's 64-bit mode is an example > of the 4GB boundary (not the best example, admittedly, but it undeniably > exists). Yes, which is what the boundary is for. But why would we default to something restrictive by default even if the driver didn't ask for it? _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu