Re: [PATCH 2/2] OMAP3: DMA: Errata: sDMA FIFO draining does not finish

Jarkko Nikula
2010-10-01T07:00:13Z

On Fri, 1 Oct 2010 09:39:06 +0300
Peter Ujfalusi <peter.ujfalusi@nokia.com> wrote:

> Implement the suggested workaround for OMAP3 regarding to sDMA draining
> issue, when the channel is disabled on the fly.
> This errata affects the following configuration:
> sDMA transfer is source synchronized
> Buffering is enabled
> SmartStandby is selected.
>
> The issue can be easily reproduced by creating overrun situation while
> recording audio.
> Either introduce load to the CPU:
> nice -19 arecord -D hw:0 -M -B 10000 -F 5000 -f dat > /dev/null & \
> dd if=/dev/urandom of=/dev/null
>
> or suspending the arecord, and resuming it:
> arecord -D hw:0 -M -B 10000 -F 5000 -f dat > /dev/null
> CTRL+Z; fg; CTRL+Z; fg; ...
>
> In case of overrun audio stops DMA, and restarts it (without reseting
> the sDMA channel). When we hit this errata in stop case (sDMA drain did
> not complete), at the coming start the sDMA will not going to be
> operational (it is still draining).
> This leads to DMA stall condition.
> On OMAP3 we can recover with sDMA channel reset, it has been observed
> that by introducing unrelated sDMA activity might also help (reading
> from MMC for example).
>
> The same errata exists for OMAP2, where the suggestion is to disable the
> buffering to avoid this type of error.
> On OMAP3 the suggestion is to set sDMA to NoStandby before disabling
> the channel, and wait for the drain to finish, than configure sDMA to
> SmartStandby again.
>
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
> ---

Acked-by: Jarkko Nikula <jhnikula@gmail.com>