linux-kernel - Re: [PATCH] dmaengine: omap-dma: Start DMA without delay for cyclic channels

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Message-ID: <20130410050441.GJ31193@intel.com>
Date:	Wed, 10 Apr 2013 10:34:41 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Dan Williams <djbw@...com>, Tony Lindgren <tony@...mide.com>,
	Jarkko Nikula <jarkko.nikula@...mer.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Felipe Balbi <balbi@...com>, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Peter Meerwald <pmeerw@...erw.net>, patches@...aro.org,
	stable@...r.kernel.org.#.v3.7+
Subject: Re: [PATCH] dmaengine: omap-dma: Start DMA without delay for
 cyclic channels

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 <pmeerw@...erw.net>
> CC: stable@...r.kernel.org  # v3.7+
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> Acked-by: Santosh Shilimkar <santosh.shilimkar@...com>
> Acked-by: Russell King <rmk+kernel@....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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