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

On 09/12/2012 03:00 PM, Russell King - ARM Linux wrote:

On Wed, Sep 12, 2012 at 02:47:07PM +0300, Peter Ujfalusi wrote:

quoted

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...

I need to look at this, but at first look we do wait for the drain in
omap_stop_dma(). We used to use omap_stop_dma/omap_start_dma for pause/resume
operations.
But sDMA also have a bit: CDPi: PAUSE_LINK_LIST which should do what we are
looking for.
Need to read the relevant parts of the TRM, but AFAIK we are using normal mode
with linked list (self linking).
I already have the patch for this, I just need to test it on HW.

-- 
P?ter