From mboxrd@z Thu Jan  1 00:00:00 1970
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
Subject: Re: [PATCH 11/11] ASoC: omap-pcm: Convert to use dmaengine
Date: Wed, 12 Sep 2012 13:00:28 +0100
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References: <1347450427-27627-1-git-send-email-peter.ujfalusi@ti.com> <1347450427-27627-12-git-send-email-peter.ujfalusi@ti.com>
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To: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>, Liam Girdwood <lrg@ti.com>, Tony Lindgren <tony@atomide.com>, Vinod Koul <vinod.koul@intel.com>, Dan Williams <djbw@fb.com>, Jarkko Nikula <jarkko.nikula@bitmer.com>, alsa-devel@alsa-project.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>, Ricardo Neri <ricardo.neri@ti.com>

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.

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.

As we have no way to know how much data may be discarded from the DMA
FIFO...