From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932131Ab2ILOGD (ORCPT ); Wed, 12 Sep 2012 10:06:03 -0400 Received: from cantor2.suse.de ([195.135.220.15]:48755 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753169Ab2ILOF7 (ORCPT ); Wed, 12 Sep 2012 10:05:59 -0400 Date: Wed, 12 Sep 2012 16:05:52 +0200 Message-ID: From: Takashi Iwai To: Russell King - ARM Linux Cc: Peter Ujfalusi , alsa-devel@alsa-project.org, Janusz Krzysztofik , Tony Lindgren , Ricardo Neri , Mark Brown , linux-kernel@vger.kernel.org, Vinod Koul , linux-arm-kernel@lists.infradead.org, Dan Williams , linux-omap@vger.kernel.org, Liam Girdwood , Jarkko Nikula Subject: Re: [alsa-devel] [PATCH 11/11] ASoC: omap-pcm: Convert to use dmaengine In-Reply-To: <20120912120028.GC28448@n2100.arm.linux.org.uk> References: <1347450427-27627-1-git-send-email-peter.ujfalusi@ti.com> <1347450427-27627-12-git-send-email-peter.ujfalusi@ti.com> <20120912120028.GC28448@n2100.arm.linux.org.uk> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/24.1 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org At Wed, 12 Sep 2012 13:00:28 +0100, Russell King - ARM Linux wrote: > > On Wed, Sep 12, 2012 at 02:47:07PM +0300, Peter Ujfalusi wrote: > > 2. Pause/Resume > > OMAP DMA engine backend does not support pausing and resuming > > an in-progress transfer. It is unclear from the specs what > > effect clearing the enable bit has on the DMA position of a > > destination synchronized transfer, and whether the transfer > > can be restarted from the exact point that it was paused (or > > whether the data in the FIFO read from memory is simply > > discarded.) > > It's worth noting that this comment (which was in my original patch) > is there to spark _comment_ and _discussion_ and should not make its > way into the final version of these patches. I agree this can be regarded as a sort of regression... > Given that suspend/resume is important on OMAP platforms, it's something > that needs to be resolved - in a way that complies with what ALSA expects. > I do not believe that the way the existing drivers do this is compliant > as the manuals imply that stopping memory->peripheral transfers results > in data being discarded from the DMA's FIFOs. As I understand it, ALSA > requires no data to be discarded. ... but in general you don't need to implement the full PAUSE and RESUME operations for PCM. For example, when SNDRV_PCM_INFO_RESUME bit isn't set, user-space is supposed to do a clean restart of the stream at wake up. So, it shouldn't break the apps severely in theory (but in practice, who knows :) > As we have no way to know how much data may be discarded from the DMA > FIFO... Yeah, the FIFO and the amount of other on flight data can be better managed. Takashi