From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?P=E9ter_Ujfalusi?= Subject: Re: [RFC] dmaengine: omap-dma: Allow DMA controller to prefetch data Date: Fri, 19 Oct 2012 14:45:55 +0200 Message-ID: <50814B83.7090203@ti.com> References: <20121018222046.GA28541@animalcreek.com> <20121018225540.GB28061@n2100.arm.linux.org.uk> <20121018232405.GA29064@animalcreek.com> <20121018233335.GC28061@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from devils.ext.ti.com ([198.47.26.153]:44469 "EHLO devils.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758601Ab2JSMqp (ORCPT ); Fri, 19 Oct 2012 08:46:45 -0400 In-Reply-To: <20121018233335.GC28061@n2100.arm.linux.org.uk> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Russell King - ARM Linux Cc: "Mark A. Greer" , linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Jarkko Nikula Hi, On 10/19/2012 01:33 AM, Russell King - ARM Linux wrote: > I would suggest getting some feedback from the ASoC people first, bef= ore > trying to invent new APIs to work around this stuff. If they can liv= e > with having prefetch enabled on OMAP then there isn't an issue here. = If > not, we need a solution to this. >=20 > I do not believe that precisely stopping and starting playback across= a > suspend/resume event is really necessary (it's desirable but the worl= d > doesn't collapse if you miss a few samples.) It could be more of an > issue for pause/resume though, but as I say, that's for ASoC people t= o > comment on. There is another issue with the prefetch in audio: we tend to like to know the position of the DMA and also to know how mu= ch data we have stored in buffers, FIFOs. This information is used by userspace= to do echo cancellation and also used by PA for example to do runtime mixing directly in the audio buffer. We have means to extract this information= from McBSP for example (and from tlv320dac33 codec) but AFAIK this informati= on can not be retrieved from sDMA. We could assume that the sDMA FIFO is kept full and report that as a 'd= elay' or do not account this information. =46or now I think the cyclic mode should not set the prefetch. If I rec= all right the cyclic mode is only used by audio at the moment. > I'm merely pointing out here that we need their feedback here before > deciding if there's anything further that needs to happen. Thanks Russell, I'll take a look at the implication of the prefetch for= audio. --=20 P=E9ter -- To unsubscribe from this list: send the line "unsubscribe linux-omap" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html