From mboxrd@z Thu Jan 1 00:00:00 1970 From: prylowski@metasoft.pl (Rafal Prylowski) Date: Thu, 22 Mar 2012 11:00:37 +0100 Subject: [PATCH] ep93xx: Implement double buffering for M2M DMA channels In-Reply-To: <4F6A78ED.3050403@gmail.com> References: <4F683B36.8090101@metasoft.pl> <4F6A78ED.3050403@gmail.com> Message-ID: <4F6AF845.9070209@metasoft.pl> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 2012-03-22 01:57, Ryan Mallon wrote: > I haven't looked through the patch yet, since I'm waiting on more > information from Mika and Hartley's testing. > > However, the commit log doesn't tell me why we want this change. Is it a > performance improvement? If so, do you have some numbers that we can > paste into the commit log? In principle, using double buffering should be faster than using only one buffer and disabling/enabling channel each time. But my measurements doesn't show any significant change. The real reason for this change is that current code is not 100% reliable in IDE-DMA (I'm planning to submit ep93xx ide driver to linux-ide soon). Although using only one buffer and DONE interrupt is simple, surprisingly we can get interrupt when M2M DMA is in DMA_BUF_ON and DMA_STALL state. If we disable the channel at this moment, we end with ata timeout. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757488Ab2CVKAw (ORCPT ); Thu, 22 Mar 2012 06:00:52 -0400 Received: from metasoft.pl ([195.149.224.191]:58407 "EHLO smtp.metasoft.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755598Ab2CVKAu (ORCPT ); Thu, 22 Mar 2012 06:00:50 -0400 X-clamdmail: clamdmail 0.18a Message-ID: <4F6AF845.9070209@metasoft.pl> Date: Thu, 22 Mar 2012 11:00:37 +0100 From: Rafal Prylowski User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0) Gecko/20120312 Thunderbird/11.0 MIME-Version: 1.0 To: Ryan Mallon CC: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "vinod.koul@intel.com" , Mika Westerberg , H Hartley Sweeten Subject: Re: [PATCH] ep93xx: Implement double buffering for M2M DMA channels References: <4F683B36.8090101@metasoft.pl> <4F6A78ED.3050403@gmail.com> In-Reply-To: <4F6A78ED.3050403@gmail.com> Content-Type: text/plain; charset=ISO-8859-2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2012-03-22 01:57, Ryan Mallon wrote: > I haven't looked through the patch yet, since I'm waiting on more > information from Mika and Hartley's testing. > > However, the commit log doesn't tell me why we want this change. Is it a > performance improvement? If so, do you have some numbers that we can > paste into the commit log? In principle, using double buffering should be faster than using only one buffer and disabling/enabling channel each time. But my measurements doesn't show any significant change. The real reason for this change is that current code is not 100% reliable in IDE-DMA (I'm planning to submit ep93xx ide driver to linux-ide soon). Although using only one buffer and DONE interrupt is simple, surprisingly we can get interrupt when M2M DMA is in DMA_BUF_ON and DMA_STALL state. If we disable the channel at this moment, we end with ata timeout.