Re: [PATCH 11/11] ASoC: omap-pcm: Convert to use dmaengine

Russell King - ARM Linux
2012-09-12T12:02:14Z

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...