linux-kernel - Re: [PATCH v2 08/13] dmaengine: at_xdmac: Move the free desc to the tail of the desc list

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Date:   Mon, 13 Dec 2021 13:37:25 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Tudor Ambarus <tudor.ambarus@...rochip.com>
Cc:     ludovic.desroches@...rochip.com, richard.genoud@...il.com,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        nicolas.ferre@...rochip.com, alexandre.belloni@...tlin.com,
        mripard@...nel.org, linux-arm-kernel@...ts.infradead.org,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH v2 08/13] dmaengine: at_xdmac: Move the free desc to the
 tail of the desc list

On 25-11-21, 11:00, Tudor Ambarus wrote:
> So that we don't use the same desc over and over again.

Please use full para in the changelog and not a continuation of the
patch title!

and why is wrong with using same desc over and over? Any benefits of not
doing so?


> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> ---
>  drivers/dma/at_xdmac.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> index 2cc9af222681..8804a86a9bcc 100644
> --- a/drivers/dma/at_xdmac.c
> +++ b/drivers/dma/at_xdmac.c
> @@ -729,7 +729,8 @@ at_xdmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  		if (!desc) {
>  			dev_err(chan2dev(chan), "can't get descriptor\n");
>  			if (first)
> -				list_splice_init(&first->descs_list, &atchan->free_descs_list);
> +				list_splice_tail_init(&first->descs_list,
> +						      &atchan->free_descs_list);
>  			goto spin_unlock;
>  		}
>  
> @@ -817,7 +818,8 @@ at_xdmac_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t buf_addr,
>  		if (!desc) {
>  			dev_err(chan2dev(chan), "can't get descriptor\n");
>  			if (first)
> -				list_splice_init(&first->descs_list, &atchan->free_descs_list);
> +				list_splice_tail_init(&first->descs_list,
> +						      &atchan->free_descs_list);
>  			spin_unlock_irqrestore(&atchan->lock, irqflags);
>  			return NULL;
>  		}
> @@ -1051,8 +1053,8 @@ at_xdmac_prep_interleaved(struct dma_chan *chan,
>  							       src_addr, dst_addr,
>  							       xt, chunk);
>  			if (!desc) {
> -				list_splice_init(&first->descs_list,
> -						 &atchan->free_descs_list);
> +				list_splice_tail_init(&first->descs_list,
> +						      &atchan->free_descs_list);
>  				return NULL;
>  			}
>  
> @@ -1132,7 +1134,8 @@ at_xdmac_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
>  		if (!desc) {
>  			dev_err(chan2dev(chan), "can't get descriptor\n");
>  			if (first)
> -				list_splice_init(&first->descs_list, &atchan->free_descs_list);
> +				list_splice_tail_init(&first->descs_list,
> +						      &atchan->free_descs_list);
>  			return NULL;
>  		}
>  
> @@ -1308,8 +1311,8 @@ at_xdmac_prep_dma_memset_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  						   sg_dma_len(sg),
>  						   value);
>  		if (!desc && first)
> -			list_splice_init(&first->descs_list,
> -					 &atchan->free_descs_list);
> +			list_splice_tail_init(&first->descs_list,
> +					      &atchan->free_descs_list);
>  
>  		if (!first)
>  			first = desc;
> @@ -1701,7 +1704,8 @@ static void at_xdmac_tasklet(struct tasklet_struct *t)
>  
>  		spin_lock_irq(&atchan->lock);
>  		/* Move the xfer descriptors into the free descriptors list. */
> -		list_splice_init(&desc->descs_list, &atchan->free_descs_list);
> +		list_splice_tail_init(&desc->descs_list,
> +				      &atchan->free_descs_list);
>  		at_xdmac_advance_work(atchan);
>  		spin_unlock_irq(&atchan->lock);
>  	}
> @@ -1850,7 +1854,8 @@ static int at_xdmac_device_terminate_all(struct dma_chan *chan)
>  	/* Cancel all pending transfers. */
>  	list_for_each_entry_safe(desc, _desc, &atchan->xfers_list, xfer_node) {
>  		list_del(&desc->xfer_node);
> -		list_splice_init(&desc->descs_list, &atchan->free_descs_list);
> +		list_splice_tail_init(&desc->descs_list,
> +				      &atchan->free_descs_list);
>  	}
>  
>  	clear_bit(AT_XDMAC_CHAN_IS_PAUSED, &atchan->status);
> -- 
> 2.25.1

-- 
~Vinod