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=-5.2 required=3.0 tests=BAYES_00, 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 82129C433DF for ; Thu, 20 Aug 2020 05:02:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3EE6720758 for ; Thu, 20 Aug 2020 05:02:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3EE6720758 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id AFD6E6B009D; Thu, 20 Aug 2020 01:02:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AADDB8D0003; Thu, 20 Aug 2020 01:02:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9EAC06B009F; Thu, 20 Aug 2020 01:02:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0072.hostedemail.com [216.40.44.72]) by kanga.kvack.org (Postfix) with ESMTP id 888526B009D for ; Thu, 20 Aug 2020 01:02:19 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 45EAB180AD817 for ; Thu, 20 Aug 2020 05:02:19 +0000 (UTC) X-FDA: 77169750798.23.roof26_2602c5e2702d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin23.hostedemail.com (Postfix) with ESMTP id 18D6A37604 for ; Thu, 20 Aug 2020 05:02:19 +0000 (UTC) X-HE-Tag: roof26_2602c5e2702d X-Filterd-Recvd-Size: 4099 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Thu, 20 Aug 2020 05:02:18 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 7DCC068BEB; Thu, 20 Aug 2020 07:02:14 +0200 (CEST) Date: Thu, 20 Aug 2020 07:02:14 +0200 From: Christoph Hellwig To: Robin Murphy Cc: Tomasz Figa , Christoph Hellwig , alsa-devel@alsa-project.org, linux-ia64@vger.kernel.org, Linux Doc Mailing List , nouveau@lists.freedesktop.org, linux-nvme@lists.infradead.org, Linux Kernel Mailing List , "James E.J. Bottomley" , linux-mm@kvack.org, Marek Szyprowski , linux-samsung-soc , Joonyoung Shim , linux-scsi@vger.kernel.org, Kyungmin Park , Ben Skeggs , Matt Porter , Linux Media Mailing List , Tom Lendacky , Pawel Osciak , Mauro Carvalho Chehab , "list@263.net:IOMMU DRIVERS" , Joerg Roedel , linux-arm-kernel@lists.infradead.org, Thomas Bogendoerfer , linux-parisc@vger.kernel.org, netdev@vger.kernel.org, Seung-Woo Kim , linux-mips@vger.kernel.org Subject: Re: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT Message-ID: <20200820050214.GA4815@lst.de> References: <20200819065555.1802761-1-hch@lst.de> <20200819065555.1802761-6-hch@lst.de> <62e4f4fc-c8a5-3ee8-c576-fe7178cb4356@arm.com> <2b32f1d8-16f7-3352-40a5-420993d52fb5@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2b32f1d8-16f7-3352-40a5-420993d52fb5@arm.com> User-Agent: Mutt/1.5.17 (2007-11-01) X-Rspamd-Queue-Id: 18D6A37604 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Aug 19, 2020 at 03:07:04PM +0100, Robin Murphy wrote: >> FWIW, I asked back in time what the plan is for non-coherent >> allocations and it seemed like DMA_ATTR_NON_CONSISTENT and >> dma_sync_*() was supposed to be the right thing to go with. [2] The >> same thread also explains why dma_alloc_pages() isn't suitable for the >> users of dma_alloc_attrs() and DMA_ATTR_NON_CONSISTENT. > > AFAICS even back then Christoph was implying getting rid of NON_CONSISTENT > and *replacing* it with something streaming-API-based - i.e. this series - > not encouraging mixing the existing APIs. It doesn't seem impossible to > implement a remapping version of this new dma_alloc_pages() for > IOMMU-backed ops if it's really warranted (although at that point it seems > like "non-coherent" vb2-dc starts to have significant conceptual overlap > with vb2-sg). You can alway vmap the returned pages from dma_alloc_pages, but it will make cache invalidation hell - you'll need to use invalidate_kernel_vmap_range and flush_kernel_vmap_range to properly handle virtually indexed caches. Or with remapping you mean using the iommu do de-scatter/gather? You can implement that trivially implement it yourself for the iommu case: { merge_boundary = dma_get_merge_boundary(dev); if (!merge_boundary || merge_boundary > chunk_size - 1) { /* can't coalesce */ return -EINVAL; } nents = DIV_ROUND_UP(total_size, chunk_size); sg = sgl_alloc(); for_each_sgl() { sg->page = __alloc_pages(get_order(chunk_size)) sg->len = chunk_size; } dma_map_sg(sg, DMA_ATTR_SKIP_CPU_SYNC); // you are guaranteed to get a single dma_addr out } Of course this still uses the scatterlist structure with its annoying mix of input and output parametes, so I'd rather not expose it as an official API at the DMA layer.