Re: [PATCH] dma: ti: k3-udma: Reset UDMA_CHAN_RT byte counters to prevent overflow

["Péter Ujfalusi" <peter.ujfalusi@gmail.com>]

On 7/4/22 14:13, Vaishnav Achath wrote:
> UDMA_CHAN_RT_*BCNT_REG stores the real-time channel bytecount statistics.
> These registers are 32-bit hardware counters and the driver uses these
> counters to monitor the operational progress status for a channel, when
> transferring more than 4GB of data it was observed that these counters
> overflow and completion calculation of a operation gets affected and the
> transfer hangs indefinitely.
> 
> This commit adds changes to decrease the byte count for every complete
> transaction so that these registers never overflow and the proper byte
> count statistics is maintained for ongoing transaction by the RT counters.
> 
> Earlier uc->bcnt used to maintain a count of the completed bytes at driver
> side, since the RT counters maintain the statistics of current transaction
> now, the maintenance of uc->bcnt is not necessary.

Thanks for the patch,

> Signed-off-by: Vaishnav Achath <vaishnav.a@ti.com>
> ---
>  drivers/dma/ti/k3-udma.c | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/dma/ti/k3-udma.c b/drivers/dma/ti/k3-udma.c
> index 2f0d2c68c93c..0f91a3e47c19 100644
> --- a/drivers/dma/ti/k3-udma.c
> +++ b/drivers/dma/ti/k3-udma.c
> @@ -300,8 +300,6 @@ struct udma_chan {
>  
>  	struct udma_tx_drain tx_drain;
>  
> -	u32 bcnt; /* number of bytes completed since the start of the channel */
> -
>  	/* Channel configuration parameters */
>  	struct udma_chan_config config;
>  
> @@ -757,6 +755,22 @@ static void udma_reset_rings(struct udma_chan *uc)
>  	}
>  }
>  
> +static void udma_decrement_byte_counters(struct udma_chan *uc, u32 val)
> +{
> +	if (uc->tchan) {
> +		udma_tchanrt_write(uc, UDMA_CHAN_RT_BCNT_REG, val);
> +		udma_tchanrt_write(uc, UDMA_CHAN_RT_SBCNT_REG, val);
> +		if (!uc->bchan)
> +			udma_tchanrt_write(uc, UDMA_CHAN_RT_PEER_BCNT_REG, val);
> +	}
> +
> +	if (uc->rchan) {
> +		udma_rchanrt_write(uc, UDMA_CHAN_RT_BCNT_REG, val);
> +		udma_rchanrt_write(uc, UDMA_CHAN_RT_SBCNT_REG, val);
> +		udma_rchanrt_write(uc, UDMA_CHAN_RT_PEER_BCNT_REG, val);
> +	}

In case of MEM_TO_MEM (or the not implemented DEV_TO_DEV) we use the
tchan's counter for position tracking, but we have the pair anyways (UDMA).
if ((uc->desc->dir == DMA_DEV_TO_MEM)
	rchan bcnt reset
else
	tchan bcnt reset

> +}
> +
>  static void udma_reset_counters(struct udma_chan *uc)
>  {
>  	u32 val;
> @@ -790,8 +804,6 @@ static void udma_reset_counters(struct udma_chan *uc)
>  		val = udma_rchanrt_read(uc, UDMA_CHAN_RT_PEER_BCNT_REG);
>  		udma_rchanrt_write(uc, UDMA_CHAN_RT_PEER_BCNT_REG, val);
>  	}
> -
> -	uc->bcnt = 0;
>  }
>  
>  static int udma_reset_chan(struct udma_chan *uc, bool hard)
> @@ -1115,8 +1127,8 @@ static void udma_check_tx_completion(struct work_struct *work)
>  		if (uc->desc) {
>  			struct udma_desc *d = uc->desc;
>  
> -			uc->bcnt += d->residue;
>  			udma_start(uc);
> +			udma_decrement_byte_counters(uc, d->residue);

Why not before udma_start()?

>  			vchan_cookie_complete(&d->vd);
>  			break;
>  		}
> @@ -1168,8 +1180,8 @@ static irqreturn_t udma_ring_irq_handler(int irq, void *data)
>  				vchan_cyclic_callback(&d->vd);
>  			} else {
>  				if (udma_is_desc_really_done(uc, d)) {
> -					uc->bcnt += d->residue;
>  					udma_start(uc);
> +					udma_decrement_byte_counters(uc, d->residue);
>  					vchan_cookie_complete(&d->vd);
>  				} else {
>  					schedule_delayed_work(&uc->tx_drain.work,
> @@ -1204,7 +1216,7 @@ static irqreturn_t udma_udma_irq_handler(int irq, void *data)
>  			vchan_cyclic_callback(&d->vd);
>  		} else {
>  			/* TODO: figure out the real amount of data */
> -			uc->bcnt += d->residue;
> +			udma_decrement_byte_counters(uc, d->residue);
>  			udma_start(uc);
>  			vchan_cookie_complete(&d->vd);
>  		}
> @@ -3809,7 +3821,6 @@ static enum dma_status udma_tx_status(struct dma_chan *chan,
>  			bcnt = udma_tchanrt_read(uc, UDMA_CHAN_RT_BCNT_REG);
>  		}
>  
> -		bcnt -= uc->bcnt;
>  		if (bcnt && !(bcnt % uc->desc->residue))
>  			residue = 0;
>  		else

-- 
Péter