Re: [RFC v2] dmaengine: omap-dma: Start DMA without delay for cyclic channels

Santosh Shilimkar
2013-04-03T11:23:12Z

On Wednesday 03 April 2013 04:47 PM, Peter Ujfalusi wrote:
> cyclic DMA is only used by audio which needs DMA to be started without a
> delay.
> If the DMA for audio is started using the tasklet we experience random
> channel switch (to be more precise: channel shift).
>
> Reported-by: Peter Meerwald <pmeerw@pmeerw.net>
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
> ---
> Hi Russell,
>
> Instead of removing the tasklet we can identify the DMA channel used by audio
> based on the cyclic flag of the channel.
> I think this can be used as a short term solution to fix the audio channel shift
> issue and later when we have the dynamic DMA channel allocation we can adjust
> the code.
>
> Regards,
> Peter
>
> drivers/dma/omap-dma.c | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c
> index 2ea3d7e..ec3fc4f 100644
> --- a/drivers/dma/omap-dma.c
> +++ b/drivers/dma/omap-dma.c
> @@ -282,12 +282,20 @@ static void omap_dma_issue_pending(struct dma_chan *chan)
>
> spin_lock_irqsave(&c->vc.lock, flags);
> if (vchan_issue_pending(&c->vc) && !c->desc) {
If you add "!c->cyclic" in above if then you can avoid
indentation change and just have else for cyclic case.

> - struct omap_dmadev *d = to_omap_dma_dev(chan->device);
> - spin_lock(&d->lock);
> - if (list_empty(&c->node))
> - list_add_tail(&c->node, &d->pending);
> - spin_unlock(&d->lock);
> - tasklet_schedule(&d->task);
> + /*
> + * c->cyclic is used only by audio and in this case the DMA need
> + * to be started without delay.
> + */
> + if (!c->cyclic) {
> + struct omap_dmadev *d = to_omap_dma_dev(chan->device);
> + spin_lock(&d->lock);
> + if (list_empty(&c->node))
> + list_add_tail(&c->node, &d->pending);
> + spin_unlock(&d->lock);
> + tasklet_schedule(&d->task);
> + } else {
> + omap_dma_start_desc(c);
> + }
> }
> spin_unlock_irqrestore(&c->vc.lock, flags);
> }
>