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=-2.5 required=3.0 tests=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 866A5C282CE for ; Tue, 9 Apr 2019 09:57:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5663620857 for ; Tue, 9 Apr 2019 09:57:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726554AbfDIJ5x (ORCPT ); Tue, 9 Apr 2019 05:57:53 -0400 Received: from verein.lst.de ([213.95.11.211]:49236 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726035AbfDIJ5w (ORCPT ); Tue, 9 Apr 2019 05:57:52 -0400 Received: by newverein.lst.de (Postfix, from userid 2407) id A73E668B02; Tue, 9 Apr 2019 11:57:40 +0200 (CEST) Date: Tue, 9 Apr 2019 11:57:40 +0200 From: "hch@lst.de" To: Thomas Hellstrom Cc: "hch@lst.de" , "torvalds@linux-foundation.org" , "linux-kernel@vger.kernel.org" , Deepak Singh Rawat , "iommu@lists.linux-foundation.org" Subject: Re: revert dma direct internals abuse Message-ID: <20190409095740.GE6827@lst.de> References: <20190408105525.5493-1-hch@lst.de> <7d5f35da4a6b58639519f0764c7edbfe4dd1ba02.camel@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7d5f35da4a6b58639519f0764c7edbfe4dd1ba02.camel@vmware.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 08, 2019 at 06:47:52PM +0000, Thomas Hellstrom wrote: > We HAVE discussed our needs, although admittedly some of my emails > ended up unanswered. And than you haven't followed up, and instead ignored the layering instructions and just commited a broken patch? > We've as you're well aware of had a discussion with the other > subsystems doing user-space DMA-buffers wanting this functionality from > the dma api (AMD graphics and RDMA people IIRC). that is a bool that > tells us whether streaming dma mappings are coherent, and I described > in detail why we couldn't use the dma_sync_* API and > dma_alloc_coherent(). And that is not at all what you either check or claim to do in the changelog (which btw, are two different things). > The other option we have is to just fail miserably without messages if > streaming DMA is not coherent, which I think the other drivers might > do... That's all I'm trying to avoid here. I'd much prefer to have the > dma API export this bool. Both DMA direct and non-DMA direct streaming mappings can be either coherent or incoherent, so your patch doesn't archive that. The commit log claims the following: "drm/vmwgfx: Improve on IOMMU detection instead of relying on intel_iommu_enabled, use the fact that the dma_map_ops::map_page != dma_direct_map_page" which has nothing to do with the fact that streaming mappings are coherent. It also is incorrect as there are direct mapping that do not use dma_direct_map_page (e.g. on ARM, or x86 with VMD).