Re: [PATCH] dma: omap-dma: add support for pause of non-cyclic transfers

[Peter Ujfalusi]

On 08/07/2015 11:41 AM, Sebastian Andrzej Siewior wrote:
> This DMA driver is used by 8250-omap on DRA7-evm. There is one
> requirement that is to pause a transfer. This is currently used on the RX
> side. It is possible that the UART HW aborted the RX (UART's RX-timeout)
> but the DMA controller starts the transfer shortly after.
> Before we can manually purge the FIFO we need to pause the transfer,
> check how many bytes it already received and terminate the transfer
> without it making any progress.
> 
> From testing on the TX side it seems that it is possible that we invoke
> pause once the transfer has completed which is indicated by the missing
> CCR_ENABLE bit but before the interrupt has been noticed. In that case the
> interrupt will come even after disabling it.
> 
> The AM572x manual says that we have to wait for the CCR_RD_ACTIVE &
> CCR_WR_ACTIVE bits to be gone before programming it again here is the
> drain loop. Also it looks like without the drain the TX-transfer makes
> sometimes progress.
> 
> One note: The pause + resume combo is broken because after resume the
> the complete transfer will be programmed again. That means the already
> transferred bytes (until the pause event) will be sent again. This is
> currently not important for my UART user because it does only pause +
> terminate.

with a short testing audio did not broke (the only user of pause/resume)
Some comments embedded.

> Cc: <stable@xxxxxxxxxxxxxxx>

Why stable? This is not fixing any bugs since the PAUSE was not allowed for
non cyclic transfers.

> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
>  drivers/dma/omap-dma.c | 54 ++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 41 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c
> index 249445c8a4c6..6b8497203caf 100644
> --- a/drivers/dma/omap-dma.c
> +++ b/drivers/dma/omap-dma.c
> @@ -299,7 +299,7 @@ static void omap_dma_start(struct omap_chan *c, struct omap_desc *d)
>  	omap_dma_chan_write(c, CCR, d->ccr | CCR_ENABLE);
>  }
>  
> -static void omap_dma_stop(struct omap_chan *c)
> +static int omap_dma_stop(struct omap_chan *c)
>  {
>  	struct omap_dmadev *od = to_omap_dma_dev(c->vc.chan.device);
>  	uint32_t val;
> @@ -342,8 +342,26 @@ static void omap_dma_stop(struct omap_chan *c)
>  
>  		omap_dma_glbl_write(od, OCP_SYSCONFIG, sysconfig);
>  	} else {
> +		int i = 0;
> +
> +		if (!(val & CCR_ENABLE))
> +			return -EINVAL;
> +
>  		val &= ~CCR_ENABLE;
>  		omap_dma_chan_write(c, CCR, val);
> +		do {
> +			val = omap_dma_chan_read(c, CCR);
> +			if (!(val & (CCR_RD_ACTIVE | CCR_WR_ACTIVE)))
> +				break;
> +			if (i > 100)

if (++i > 100)
	break;
to avoid infinite loop?


> +				break;
> +			udelay(5);
> +		} while (1);
> +
> +		if (val & (CCR_RD_ACTIVE | CCR_WR_ACTIVE))

if (i > 100) ?



> +			dev_err(c->vc.chan.device->dev,
> +				"DMA drain did not complete on lch %d\n",
> +				c->dma_ch);
>  	}
>  
>  	mb();
> @@ -358,6 +376,7 @@ static void omap_dma_stop(struct omap_chan *c)
>  
>  		omap_dma_chan_write(c, CLNK_CTRL, val);
>  	}
> +	return 0;
>  }
>  
>  static void omap_dma_start_sg(struct omap_chan *c, struct omap_desc *d,
> @@ -728,6 +747,8 @@ static enum dma_status omap_dma_tx_status(struct dma_chan *chan,
>  	} else {
>  		txstate->residue = 0;
>  	}
> +	if (ret == DMA_IN_PROGRESS && c->paused)
> +		ret = DMA_PAUSED;
>  	spin_unlock_irqrestore(&c->vc.lock, flags);
>  
>  	return ret;
> @@ -1053,28 +1074,33 @@ static int omap_dma_terminate_all(struct dma_chan *chan)
>  static int omap_dma_pause(struct dma_chan *chan)
>  {
>  	struct omap_chan *c = to_omap_dma_chan(chan);
> +	struct omap_dmadev *od = to_omap_dma_dev(chan->device);
> +	unsigned long flags;
> +	int ret = -EINVAL;
>  
> -	/* Pause/Resume only allowed with cyclic mode */
> -	if (!c->cyclic)
> -		return -EINVAL;
> +	spin_lock_irqsave(&od->irq_lock, flags);
>  
> -	if (!c->paused) {
> -		omap_dma_stop(c);
> -		c->paused = true;
> +	if (!c->paused && c->desc) {
> +		ret = omap_dma_stop(c);
> +		if (!ret)
> +			c->paused = true;
>  	}
>  
> -	return 0;
> +	spin_unlock_irqrestore(&od->irq_lock, flags);
> +
> +	return ret;
>  }
>  
>  static int omap_dma_resume(struct dma_chan *chan)
>  {
>  	struct omap_chan *c = to_omap_dma_chan(chan);
> +	struct omap_dmadev *od = to_omap_dma_dev(chan->device);
> +	unsigned long flags;
> +	int ret = -EINVAL;
>  
> -	/* Pause/Resume only allowed with cyclic mode */
> -	if (!c->cyclic)
> -		return -EINVAL;
> +	spin_lock_irqsave(&od->irq_lock, flags);
>  
> -	if (c->paused) {
> +	if (c->paused && c->desc) {
>  		mb();
>  
>  		/* Restore channel link register */
> @@ -1082,9 +1108,11 @@ static int omap_dma_resume(struct dma_chan *chan)
>  
>  		omap_dma_start(c, c->desc);
>  		c->paused = false;
> +		ret = 0;
>  	}
> +	spin_unlock_irqrestore(&od->irq_lock, flags);
>  
> -	return 0;
> +	return ret;
>  }
>  
>  static int omap_dma_chan_init(struct omap_dmadev *od)
> 


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