From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753665AbaATNIz (ORCPT ); Mon, 20 Jan 2014 08:08:55 -0500 Received: from mga09.intel.com ([134.134.136.24]:1087 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751627AbaATNIx (ORCPT ); Mon, 20 Jan 2014 08:08:53 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.95,690,1384329600"; d="scan'208";a="461627734" Date: Mon, 20 Jan 2014 17:37:14 +0530 From: Vinod Koul To: "Shevchenko, Andriy" Cc: Andy Shevchenko , "Chew, Chiau Ee" , Viresh Kumar , "Williams, Dan J" , "dmaengine@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] dma: dw: Add suspend and resume handling for PCI mode DW_DMAC. Message-ID: <20140120120714.GF26823@intel.com> References: <1386684373-24753-1-git-send-email-chiau.ee.chew@intel.com> <20131210101025.GF29580@intel.com> <1386676582.1871.137.camel@smile> <604BF5F4C5D71041942BC7E84ED659EA01520785@PGSMSX103.gar.corp.intel.com> <20131218154955.GF16227@intel.com> <1387450289.1871.240.camel@smile> <20140120092501.GS26823@intel.com> <1390222075.7619.29.camel@smile> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1390222075.7619.29.camel@smile> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 20, 2014 at 06:17:56PM +0530, Shevchenko, Andriy wrote: > On Mon, 2014-01-20 at 14:55 +0530, Vinod Koul wrote: > > On Thu, Dec 19, 2013 at 12:51:29PM +0200, Andy Shevchenko wrote: > > > On Wed, 2013-12-18 at 21:19 +0530, Vinod Koul wrote: > > > > On Mon, Dec 16, 2013 at 01:51:47PM +0530, Chew, Chiau Ee wrote: > > > > > > > > As mentioned by Andy, we are using *_noirq verion of suspend/resume PM > > > > > callback whereby the callbacks would be executed after IRQ handlers have been > > > > > disabled. If using SET_SYSTEM_SLEEP_PM_OPS, it would be the normal > > > > > suspend/resume PM callback. Looking at the Desginware DMAC platform code > > > > > (drivers/dma/dw/platform.c), it is using the *_noirq suspend/resume PM > > > > > callback. Is it advisable to use the normal suspend/resume PM callback instead > > > > > of *_noirq suspend/PM callback? > > > > > > > > i dont see a reason why we need the noirq versions > > > > > > Okay. I imagine the following use case. > > > > > > For example we have compiled in DMA driver (dw_dmac) along with, for > > > example, SPI driver. > > > > > > System was scheduled to go sleep. > > > > > > An order of calling IIUC might be DMA first, then SPI (since they are > > > not in parent / child relations). > > > > > > What was happened when SPI would like to do a DMA transfer and DMA is > > > going to sleep? I'm trying to understand if this is a case. > > In that case how does no irq version help us? > > It guarantees that we have no user of DMA anymore, since there is no > interrupt going on. well how is that. It will gaurantee that there wont be interrupt. User can still submit a transaction or another transaction will be in progress... > > For these cases, I have been using suspend_late. Since the dmaengine driver is > > providing service to other clients (SPI), it needs to esnure that it suspends > > after SPI using suspend_late and resume using resume_early. That way dma is > > availble whenever the client is active > > suspend_late is working in context that interrupt handler may be > invoked. Thus, to have DMA driver be properly shut down we have to > wait / terminate possible ongoing transfer. Well client is already suspended via .suspend. So where is the transaction :) > > It seems for me all DMA drivers that are using > system .suspend()/.resume() are potentially buggy. Yup! -- ~Vinod