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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 7D448C433E0 for ; Mon, 22 Jun 2020 15:54:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 573D020760 for ; Mon, 22 Jun 2020 15:54:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592841287; bh=oRJB6h/bS+tqbd9R39cS2329vCq3WIUuVv0P5qICFUs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=t6YSHAr3X1F9CaNNkslekHJGPfTyviE8hhltkTOpHBXQfxJ0Pa6MT3hRsD3xhk06o qhefp/btz3BqUEefSrGf5C2iRdS2EsU4OAsoyWh1rlaqY287eFFbAPn/cUImbKVtNv dhnXtvfUCXefdRIOrzi8Xr8blhLNB3n7eum4Zm24= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729266AbgFVPyr (ORCPT ); Mon, 22 Jun 2020 11:54:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:54936 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726328AbgFVPyq (ORCPT ); Mon, 22 Jun 2020 11:54:46 -0400 Received: from localhost (unknown [171.61.66.58]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 53FBF2074D; Mon, 22 Jun 2020 15:54:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592841286; bh=oRJB6h/bS+tqbd9R39cS2329vCq3WIUuVv0P5qICFUs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=1rAAOtWug0zRuuAKt9uYzXZhuiodYywEsoqay8UQK3SGp4XmBOkmVS428PppVFfJK y+vATJ5E/6KVsCPPVP8gJwSOqDwxnogBkP0VDTbYzkWSkddu19cGnxO7R8uK4BKSly uwZBbjQd5lWiKAzjITZLVpbTBPJ4a2wHK2HK2n10= Date: Mon, 22 Jun 2020 21:24:40 +0530 From: Vinod Koul To: Thomas Ruf Cc: Federico Vaga , Dave Jiang , Dan Williams , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: DMA Engine: Transfer From Userspace Message-ID: <20200622155440.GM2324254@vkoul-mobl> References: <5614531.lOV4Wx5bFT@harkonnen> <20200621072457.GA2324254@vkoul-mobl> <20200621203634.y3tejmh6j4knf5iz@cwe-513-vol689.cern.ch> <20200622044733.GB2324254@vkoul-mobl> <419762761.402939.1592827272368@mailbusiness.ionos.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <419762761.402939.1592827272368@mailbusiness.ionos.de> Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org On 22-06-20, 14:01, Thomas Ruf wrote: > > On 22 June 2020 at 06:47 Vinod Koul wrote: > > > > On 21-06-20, 22:36, Federico Vaga wrote: > > > On Sun, Jun 21, 2020 at 12:54:57PM +0530, Vinod Koul wrote: > > > > On 19-06-20, 16:31, Dave Jiang wrote: > > > > > > > > > > > > > > > On 6/19/2020 3:47 PM, Federico Vaga wrote: > > > > > > Hello, > > > > > > > > > > > > is there the possibility of using a DMA engine channel from userspace? > > > > > > > > > > > > Something like: > > > > > > - configure DMA using ioctl() (or whatever configuration mechanism) > > > > > > - read() or write() to trigger the transfer > > > > > > > > > > > > > > > > I may have supposedly promised Vinod to look into possibly providing > > > > > something like this in the future. But I have not gotten around to do that > > > > > yet. Currently, no such support. > > > > > > > > And I do still have serious reservations about this topic :) Opening up > > > > userspace access to DMA does not sound very great from security point of > > > > view. > > > > > > I was thinking about a dedicated module, and not something that the DMA engine > > > offers directly. You load the module only if you need it (like the test module) > > > > But loading that module would expose dma to userspace. > > > > > > > Federico, what use case do you have in mind? > > > > > > Userspace drivers > > > > more the reason not do do so, why cant a kernel driver be added for your > > usage? > > by chance i have written a driver allowing dma from user space using a memcpy like interface ;-) > now i am trying to get this code upstream but was hit by the fact that DMA_SG is gone since Aug 2017 :-( > > just let me introduce myself and the project: > - coding in C since '91 > - coding in C++ since '98 > - a lot of stuff not relevant for this ;-) > - working as a freelancer since Nov '19 > - implemented a "dma-sg-proxy" driver for my client in Mar/Apr '20 to copy camera frames from uncached memory to cached memory using a second dma on a Zynq platform > - last week we figured out that we can not upgrade from "Xilinx 2019.2" (kernel 4.19.x) to "2020.1" (kernel 5.4.x) because the DMA_SG interface is gone > - subscribed to dmaengine on friday, saw the start of this discussion on saturday > - talked to my client today if it is ok to try to revive DMA_SG and get our driver upstream to avoid such problems in future DMA_SG was removed as it had no users, if we have a user (in-kernel) we can certainly revert that removal patch. > > here the struct for the ioctl: > > typedef struct { > unsigned int struct_size; > const void *src_user_ptr; > void *dst_user_ptr; > unsigned long length; > unsigned int timeout_in_ms; > } dma_sg_proxy_arg_t; Again, am not convinced opening DMA to userspace like this is a great idea. Why not have Xilinx camera driver invoke the dmaengine and do DMA_SG ? -- ~Vinod