From mboxrd@z Thu Jan 1 00:00:00 1970 From: Liam Girdwood Subject: Re: [PATCH] ASoC: davinci-pcm: comments for the conversion to BATCH mode Date: Wed, 25 May 2011 15:19:39 +0100 Message-ID: <4DDD0FFB.1060405@ti.com> References: <4DDCD16C.1080702@ti.com> <1306330042-16714-1-git-send-email-bengardiner@nanometrics.ca> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from arroyo.ext.ti.com (arroyo.ext.ti.com [192.94.94.40]) by alsa0.perex.cz (Postfix) with ESMTP id 5667910380F for ; Wed, 25 May 2011 16:19:47 +0200 (CEST) In-Reply-To: <1306330042-16714-1-git-send-email-bengardiner@nanometrics.ca> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: Ben Gardiner Cc: Steven Faludi , "alsa-devel@alsa-project.org" , Mark Brown , "Nori, Sekhar" , "davinci-linux-open-source@linux.davincidsp.com" , Troy Kisky List-Id: alsa-devel@alsa-project.org On 25/05/11 14:27, Ben Gardiner wrote: > In the previous commit 'ASoC: davinci-pcm: convert to BATCH mode', the phase > offset of 2 was mentioned in the commit message but not well commented in the > source. > > Add descriptive comments of the phase offset with and without ping-pong > buffers enabled. > > Signed-off-by: Ben Gardiner > > --- > sound/soc/davinci/davinci-pcm.c | 19 +++++++++++++++++++ > 1 files changed, 19 insertions(+), 0 deletions(-) > > diff --git a/sound/soc/davinci/davinci-pcm.c b/sound/soc/davinci/davinci-pcm.c > index fa8fc61..c9e0320 100644 > --- a/sound/soc/davinci/davinci-pcm.c > +++ b/sound/soc/davinci/davinci-pcm.c > @@ -605,6 +605,18 @@ static int davinci_pcm_prepare(struct snd_pcm_substream *substream) > print_buf_info(prtd->asp_link[0], "asp_link[0]"); > print_buf_info(prtd->asp_link[1], "asp_link[1]"); > > + /* > + * There is a phase offset of 2 periods between the position > + * used by dma setup and the position reported in the pointer > + * function. > + * > + * The phase offset, when not using ping-pong buffers, is due to > + * the two consecutive calls to davinci_pcm_enqueue_dma() below. > + * > + * Whereas here, with ping-pong buffers, the phase is due to > + * there being an entire buffer transfer complete before the > + * first dma completion event triggers davinci_pcm_dma_irq(). > + */ > davinci_pcm_period_elapsed(substream); > davinci_pcm_period_elapsed(substream); > > @@ -631,6 +643,13 @@ davinci_pcm_pointer(struct snd_pcm_substream *substream) > int asp_count; > unsigned int period_size = snd_pcm_lib_period_bytes(substream); > > + /* > + * There is a phase offset of 2 periods between the position used by dma > + * setup and the position reported in the pointer function. Either +2 in > + * the dma setup or -2 here in the pointer function (with wrapping, > + * both) accounts for this offset -- choose the latter since it makes > + * the first-time setup clearer. > + */ > spin_lock(&prtd->lock); > asp_count = prtd->period - 2; > spin_unlock(&prtd->lock); Acked-by: Liam Girdwood