From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751427AbaEGTP4 (ORCPT ); Wed, 7 May 2014 15:15:56 -0400 Received: from smtp-out-029.synserver.de ([212.40.185.29]:1027 "EHLO smtp-out-016.synserver.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751010AbaEGTPx (ORCPT ); Wed, 7 May 2014 15:15:53 -0400 X-SynServer-TrustedSrc: 1 X-SynServer-AuthUser: lars@metafoo.de X-SynServer-PPID: 4471 Message-ID: <536A865B.1060007@metafoo.de> Date: Wed, 07 May 2014 21:15:39 +0200 From: Lars-Peter Clausen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131103 Icedove/17.0.10 MIME-Version: 1.0 To: Stephen Warren CC: Christopher Freeman , ldewangan@nvidia.com, swarren@nvidia.com, vinod.koul@intel.com, dan.j.williams@intel.com, dmaengine@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 3/3] dma: tegra: avoid int overflow for transferred count References: <1399411343-12222-1-git-send-email-cfreeman@nvidia.com> <1399411343-12222-4-git-send-email-cfreeman@nvidia.com> <536A61A3.3050601@wwwdotorg.org> In-Reply-To: <536A61A3.3050601@wwwdotorg.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/07/2014 06:38 PM, Stephen Warren wrote: > On 05/06/2014 03:22 PM, Christopher Freeman wrote: >> bytes_transferred will overflow during long audio playbacks. Since >> the driver only ever consults this value modulo bytes_requested, store the >> value modulo bytes_requested. > > The audio driver may only interpret the value modulo bytes_requested, > but what about other drivers such as the high-speed UART (and SPI?) drivers? > > What is the dmaengine API's design requirement here, and what do other > dmaengine drivers do. If it's to store the modulo, then I'm fine with > this change. Yep, this part of the API. The residue should be between transfer length and 0. While 0 is special and should only be returned if the transfer has finished. For cyclic transfers this means it should never be zero. So if transferred_bytes is incremented modulo length and residue is length - transferred_bytes you get the correct result.