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Mon, 22 Jun 2020 08:57:27 +0200 Date: Mon, 22 Jun 2020 08:57:27 +0200 From: Federico Vaga To: Vinod Koul CC: Dave Jiang , Dan Williams , , Subject: Re: DMA Engine: Transfer From Userspace Message-ID: <20200622065727.ywbnevdhjs7kizfc@cwe-513-vol689.cern.ch> References: <5614531.lOV4Wx5bFT@harkonnen> <20200621072457.GA2324254@vkoul-mobl> <20200621203634.y3tejmh6j4knf5iz@cwe-513-vol689.cern.ch> <20200622044733.GB2324254@vkoul-mobl> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed Content-Disposition: inline In-Reply-To: <20200622044733.GB2324254@vkoul-mobl> X-Originating-IP: [2001:1458:d00:7::100:1c8] X-EOPAttributedMessage: 0 X-Forefront-Antispam-Report: CIP:188.184.36.50;CTRY:CH;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:cernmxgwlb4.cern.ch;PTR:cernmx11.cern.ch;CAT:NONE;SFTY:;SFS:(396003)(376002)(136003)(346002)(39860400002)(46966005)(53546011)(316002)(82310400002)(54906003)(83380400001)(426003)(336012)(478600001)(6916009)(44832011)(7636003)(82740400003)(356005)(47076004)(8936002)(70206006)(16526019)(186003)(26005)(86362001)(5660300002)(8676002)(4326008)(1076003)(70586007)(7696005)(2906002)(55016002);DIR:OUT;SFP:1101; X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: dbaf38d3-bf89-4b4f-a0f9-08d8167987fa X-MS-TrafficTypeDiagnostic: HE1PR0601MB2075: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8273; X-Forefront-PRVS: 0442E569BC X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 1QqERMWt1hd2PzJRjiJSUOeJ9W0zzH6c+tyUowPBy+esUOZjsaB30nWiUdx04R80ADg/cjXAv9eroc+ble15kFVIuXWYlBeTa2PujtmJHhjSH5dRuoyFVuKyadHq/+in/I6A4GPJfLHDPqY/+GZ8bSK+OxgAAORRexJLRbrUxQgNatRMyqKW2+pflkxbSuI+VigXN3fAHBOcy3ONZZ7xmlQiq3Q8Ne7g8ZplYbHywZ2TFGtvZ+Yatg2CFMm5ckMkDMzh2f2mC8/FzMtDf7GZX+qmJIyqPmg+sirXuXIFVA2cA7EqHyIA9O6gmLSBLQEwi2zKPK65672OvAv8QqxW3PViSPYCEPTVNKERKYzf6+kU65GM75GU7Sxljv+YOhp/ycnW9kzNkQCdUdc/em3s9g== X-OriginatorOrg: cern.ch X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Jun 2020 06:57:29.8359 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: dbaf38d3-bf89-4b4f-a0f9-08d8167987fa X-MS-Exchange-CrossTenant-Id: c80d3499-4a40-4a8c-986e-abce017d6b19 X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=c80d3499-4a40-4a8c-986e-abce017d6b19;Ip=[188.184.36.50];Helo=[cernmxgwlb4.cern.ch] X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: HE1PR0601MB2075 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 22, 2020 at 10:17:33AM +0530, 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. Of course, but users *should* know what they are doing ... right? ^_^' >> >> > 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? Yes of course, I was just wandering if there was a kernel API. >-- >~Vinod