Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759290AbZDAJLf (ORCPT ); Wed, 1 Apr 2009 05:11:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750903AbZDAJLZ (ORCPT ); Wed, 1 Apr 2009 05:11:25 -0400 Received: from relay.atmel.no ([80.232.32.139]:56718 "EHLO relay.atmel.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751191AbZDAJLY (ORCPT ); Wed, 1 Apr 2009 05:11:24 -0400 Date: Wed, 1 Apr 2009 11:11:16 +0200 From: Hans-Christian Egtvedt To: Haavard Skinnemoen Cc: "Sosnowski, Maciej" , "linux-kernel@vger.kernel.org" , "Williams, Dan J" Subject: Re: [PATCH 2/2] dw_dmac: add cyclic API to DW DMA driver Message-ID: <20090401111116.7c604530@hcegtvedt> In-Reply-To: <20090401102830.6a749ad2@hskinnemoen-d830> References: <1237894506-11622-1-git-send-email-hans-christian.egtvedt@atmel.com> <1237894506-11622-2-git-send-email-hans-christian.egtvedt@atmel.com> <129600E5E5FB004392DDC3FB599660D790F8C3F0@irsmsx504.ger.corp.intel.com> <20090401102830.6a749ad2@hskinnemoen-d830> Organization: Atmel X-Mailer: Claws Mail 3.6.1 (GTK+ 2.16.0; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1678 Lines: 46 On Wed, 1 Apr 2009 10:28:30 +0200 Haavard Skinnemoen wrote: > Sosnowski, Maciej wrote: > > > +void dw_dma_cyclic_stop(struct dma_chan *chan) > > > +{ > > > + struct dw_dma_chan *dwc = to_dw_dma_chan(chan); > > > + struct dw_dma *dw = > > > to_dw_dma(dwc->chan.device); + > > > + channel_clear_bit(dw, CH_EN, dwc->mask); > > > + while (dma_readl(dw, CH_EN) & dwc->mask) > > > + cpu_relax(); > > > +} > > > > Don't you need locks in dw_dma_cyclic_stop? > > Good question. On one hand, if cyclic_start() can race with > cyclic_stop(), the client probably has more serious issues to deal > with. On the other hand, if something ever manages to set the CH_EN > bit at the wrong moment, the loop may never finish. > > So it's probably safest to wrap it in spin_lock_bh(). You should > probably add a note that this function can not be called from > interrupt context too. > The problem then is when calling cyclic_stop from the trigger function in an ALSA driver. http://www.kernel.org/pub/linux/kernel/people/tiwai/docs/writing-an-alsa-driver/ch05s06.html#pcm-interface-operators-trigger-callback This callback is atomic, and with interrupts disabled. So using spin_lock_bh() is AFAICT not allowed. I am going to brush up the interface and document that the _stop and _start interface has to be called with interrupts disabled. Will post a v2 shortly. -- Best regards, Hans-Christian Egtvedt -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/