From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753334Ab2AGTVw (ORCPT ); Sat, 7 Jan 2012 14:21:52 -0500 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:33347 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753176Ab2AGTVv (ORCPT ); Sat, 7 Jan 2012 14:21:51 -0500 Date: Sat, 7 Jan 2012 19:21:12 +0000 From: Russell King - ARM Linux To: David Brown Cc: Daniel Walker , Ravi Kumar V , vinod.koul@intel.com, dan.j.williams@intel.com, arnd@arndb.de, linux-arch@vger.kernel.org, bryanh@codeaurora.org, tsoni@qualcomm.com, johlstei@qualcomm.com, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 2/2] msm: DMAEngine: Add DMAEngine driver based on old MSM DMA APIs Message-ID: <20120107192112.GB13181@n2100.arm.linux.org.uk> References: <1325854052-21402-1-git-send-email-kumarrav@codeaurora.org> <1325854052-21402-3-git-send-email-kumarrav@codeaurora.org> <1325901569.10425.14.camel@m0nster> <20120107185443.GA19216@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120107185443.GA19216@codeaurora.org> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 07, 2012 at 10:54:43AM -0800, David Brown wrote: > On Fri, Jan 06, 2012 at 05:59:29PM -0800, Daniel Walker wrote: > > > > diff --git a/drivers/dma/msm-dma.c b/drivers/dma/msm-dma.c > > > new file mode 100644 > > > index 0000000..51d9a2b > > > --- /dev/null > > > +++ b/drivers/dma/msm-dma.c > > > ... > > > +static void msm_chan_desc_cleanup(struct msm_dma_chan *chan) > > > +{ > > > + struct msm_dma_desc_sw *desc, *_desc; > > > + unsigned long flags; > > > + > > > + dev_dbg(chan->dev, "Cleaning completed descriptor of channel %d\n", > > > + chan->chan_id); > > > + spin_lock_irqsave(&chan->lock, flags); > > > + > > > + list_for_each_entry_safe(desc, _desc, &chan->active_list, node) { > > > + dma_async_tx_callback callback; > > > + void *callback_param; > > > + > > > + if (msm_dma_desc_status(chan, desc) == DMA_IN_PROGRESS) > > > + break; > > > + > > > + /* Remove from the list of running transactions */ > > > + list_del(&desc->node); > > > + > > > + /* Run the link descriptor callback function */ > > > + callback = desc->async_tx.callback; > > > + callback_param = desc->async_tx.callback_param; > > > + if (callback) { > > > + spin_unlock_irqrestore(&chan->lock, flags); > > > + callback(callback_param); > > > > Are you sure unlocking here is safe? at_hdmac.c holds the lock the > > entire time, and fsldma.c deletes the entire list, then runs the > > operations. > > Good catch. > > According to a comment in at_hdmac.c, it is safe to hold the lock > while calling the callbacks, so that's probably the easiest solution. > I suspect that you've got something in another driver expecting the > lock to be released, and that might have to be changed. It is _not_ safe to hold the lock while calling callbacks. Please refer to the DMA engine documentation, found here: Documentation/dmaengine.txt section 3: Note: Although the async_tx API specifies that completion callback routines cannot submit any new operations, this is not the case for slave/cyclic DMA. For slave DMA, the subsequent transaction may not be available for submission prior to callback function being invoked, so slave DMA callbacks are permitted to prepare and submit a new transaction. For cyclic DMA, a callback function may wish to terminate the DMA via dmaengine_terminate_all(). * Therefore, it is important that DMA engine drivers drop any * locks before calling the callback function which may cause a * deadlock. Note that callbacks will always be invoked from the DMA engines tasklet, never from interrupt context.