Re: [PATCH 4/5] dmaengine: xdmac: Rework the chaining logic

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On Tue, Apr 28, 2015 at 11:03:22AM +0200, Maxime Ripard wrote:
> So far, we were setting the NDE bit in our descriptors through some logic to
> try to see if we were the last descriptor in the chain.
> 
> However, that was turning out to be rather complex to get right, while this
> information is also available when we actually chain a new descriptor after an
> already existing one.
> 
> Simplify this by never setting NDE unless when we actually chain a descriptor.
> 
> Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx>

With correction suggested by Vinod
Acked-by: Ludovic Desroches <ludovic.desroches@xxxxxxxxx>

> ---
>  drivers/dma/at_xdmac.c | 41 ++++++++++++++++++++---------------------
>  1 file changed, 20 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> index cbeadeeed9c0..67e566b2b24f 100644
> --- a/drivers/dma/at_xdmac.c
> +++ b/drivers/dma/at_xdmac.c
> @@ -471,6 +471,20 @@ static struct at_xdmac_desc *at_xdmac_get_desc(struct at_xdmac_chan *atchan)
>  	return desc;
>  }
>  
> +static void at_xdmac_queue_desc(struct dma_chan *chan,
> +				struct at_xdmac_desc *prev,
> +				struct at_xdmac_desc *desc)
> +{
> +	if (!prev || !desc)
> +		return;
> +
> +	prev->lld.mbr_nda = desc->tx_dma_desc.phys;
> +	prev->lld.mbr_ubc |= AT_XDMAC_MBR_UBC_NDE;
> +
> +	dev_dbg(chan2dev(chan),	"%s: chain lld: prev=0x%p, mbr_nda=0x%08x\n",
> +		__func__, prev, prev->lld.mbr_nda);
> +}
> +
>  static struct dma_chan *at_xdmac_xlate(struct of_phandle_args *dma_spec,
>  				       struct of_dma *of_dma)
>  {
> @@ -627,19 +641,14 @@ at_xdmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV2			/* next descriptor view */
>  			| AT_XDMAC_MBR_UBC_NDEN					/* next descriptor dst parameter update */
>  			| AT_XDMAC_MBR_UBC_NSEN					/* next descriptor src parameter update */
> -			| (i == sg_len - 1 ? 0 : AT_XDMAC_MBR_UBC_NDE)		/* descriptor fetch */
>  			| (len >> fixed_dwidth);				/* microblock length */
>  		dev_dbg(chan2dev(chan),
>  			 "%s: lld: mbr_sa=%pad, mbr_da=%pad, mbr_ubc=0x%08x\n",
>  			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
>  
>  		/* Chain lld. */
> -		if (prev) {
> -			prev->lld.mbr_nda = desc->tx_dma_desc.phys;
> -			dev_dbg(chan2dev(chan),
> -				 "%s: chain lld: prev=0x%p, mbr_nda=%pad\n",
> -				 __func__, prev, &prev->lld.mbr_nda);
> -		}
> +		if (prev)
> +			at_xdmac_queue_desc(chan, prev, desc);
>  
>  		prev = desc;
>  		if (!first)
> @@ -714,7 +723,6 @@ at_xdmac_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t buf_addr,
>  		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV1
>  			| AT_XDMAC_MBR_UBC_NDEN
>  			| AT_XDMAC_MBR_UBC_NSEN
> -			| AT_XDMAC_MBR_UBC_NDE
>  			| period_len >> at_xdmac_get_dwidth(desc->lld.mbr_cfg);
>  
>  		dev_dbg(chan2dev(chan),
> @@ -722,12 +730,8 @@ at_xdmac_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t buf_addr,
>  			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
>  
>  		/* Chain lld. */
> -		if (prev) {
> -			prev->lld.mbr_nda = desc->tx_dma_desc.phys;
> -			dev_dbg(chan2dev(chan),
> -				 "%s: chain lld: prev=0x%p, mbr_nda=%pad\n",
> -				 __func__, prev, &prev->lld.mbr_nda);
> -		}
> +		if (prev)
> +			at_xdmac_queue_desc(chan, prev, desc);
>  
>  		prev = desc;
>  		if (!first)
> @@ -850,7 +854,6 @@ at_xdmac_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
>  		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV2
>  			| AT_XDMAC_MBR_UBC_NDEN
>  			| AT_XDMAC_MBR_UBC_NSEN
> -			| (remaining_size ? AT_XDMAC_MBR_UBC_NDE : 0)
>  			| ublen;
>  		desc->lld.mbr_cfg = chan_cc;
>  
> @@ -859,12 +862,8 @@ at_xdmac_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
>  			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc, desc->lld.mbr_cfg);
>  
>  		/* Chain lld. */
> -		if (prev) {
> -			prev->lld.mbr_nda = desc->tx_dma_desc.phys;
> -			dev_dbg(chan2dev(chan),
> -				 "%s: chain lld: prev=0x%p, mbr_nda=0x%08x\n",
> -				 __func__, prev, prev->lld.mbr_nda);
> -		}
> +		if (prev)
> +			at_xdmac_queue_desc(chan, prev, desc);
>  
>  		prev = desc;
>  		if (!first)
> -- 
> 2.3.6
> 
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