[PATCH 2/3] dma: mxs-dma: Track number of irqs for callback

[mkl@pengutronix.de (Marc Kleine-Budde)]

On 09/26/2013 05:06 PM, Markus Pargmann wrote:
> Currently there is one tasklet scheduled for all interrupts between two
> mxs_dma_tasklet calls for one channel. With more than one interrupts,
> the tasklet is only called once.
> 
> Using low latency audio playback, can lead to problems. When using
> sound/soc/soc-dmaengine-pcm.c, the dmaengine_pcm_dma_complete relies on
> being called for each interrupt that occures. This function is the
> callback which is called from the mxs-dma driver in mxs_dma_tasklet.
> This can cause wrong position counters and can lead to a wrong DMA
> buffer offset. In this situation the DMA engine and pcm lib may write
> and read from the same buffer segment.
> 
> This patch adds a locked per-channel irq counter and calls the callback
> function in a loop for irq-counter times.

If you have two counters, one for generated interrupts and one for
handled interrupts, you don't need any locking.

Marc

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