On Tue, Apr 09, 2013 at 04:33:06PM +0200, 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 <pme...@pmeerw.net>
> CC: sta...@vger.kernel.org # v3.7+
> Signed-off-by: Peter Ujfalusi <peter.ujfal...@ti.com>
> Acked-by: Santosh Shilimkar <santosh.shilim...@ti.com>
> Acked-by: Russell King <rmk+ker...@arm.linux.org.uk>
> ---
> Hi Vinod,
>
> Would it be possible to send this patch for 3.9. The channel shift (or switch)
> issue in audio has been noticed recently and it turns out that it has been
> present since 3.7 kernel.
> It would be great if 3.9 kernel could work correctly out of box...
Applied to fixes. I will send this to linus in a day...
--
~Vinod
>
> Changes since RFCv2:
> - added Acked-by from Santosh and Russell
>
> Thank you,
> 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) {
> - 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);
> }
> --
> 1.8.1.5
>
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