Re: [PATCH v6 04/10] dmaengine: dw: extract hardware-LLP residue calculation

[Frank Li]

On Tue, Nov 03, 2026 at 03:26:06PM -0700, James Hilliard wrote:
> From: Serge Semin <fancer.lancer@xxxxxxxxx>
>
> Move the hardware-LLP residue calculation into
> dwc_get_hard_llp_desc_residue() so it can be reused independently of
> completion handling.
>
> Keep the scanner's LLP snapshot, descriptor updates and early returns
> unchanged. The helper reports whether it found the current descriptor,
> including when that descriptor has zero residue, rather than using the
> residue value as a completion indication.
>
> Signed-off-by: Serge Semin <fancer.lancer@xxxxxxxxx>
> [james: extract the calculation without changing scanner behavior]
> Signed-off-by: James Hilliard <james.hilliard1@xxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

>  drivers/dma/dw/core.c | 58 +++++++++++++++++++++++++++++----------------------
>  1 file changed, 33 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
> index 2d69fab06601..5a1caca7ad68 100644
> --- a/drivers/dma/dw/core.c
> +++ b/drivers/dma/dw/core.c
> @@ -267,6 +267,38 @@ static inline u32 dwc_get_sent(struct dw_dma_chan *dwc)
>  	return dw->block2bytes(dwc, ctlhi, ctllo >> 4 & 7);
>  }
>
> +static bool dwc_get_hard_llp_desc_residue(struct dw_dma_chan *dwc,
> +				       struct dw_desc *desc, dma_addr_t llp)
> +{
> +	struct dw_desc *child;
> +
> +	/* Initial residue value */
> +	desc->residue = desc->total_len;
> +
> +	/* Check first descriptors addr */
> +	if (desc->txd.phys == DWC_LLP_LOC(llp))
> +		return true;
> +
> +	/* Check first descriptors llp */
> +	if (lli_read(desc, llp) == llp) {
> +		/* This one is currently in progress */
> +		desc->residue -= dwc_get_sent(dwc);
> +		return true;
> +	}
> +
> +	desc->residue -= desc->len;
> +	list_for_each_entry(child, &desc->tx_list, desc_node) {
> +		if (lli_read(child, llp) == llp) {
> +			/* Currently in progress */
> +			desc->residue -= dwc_get_sent(dwc);
> +			return true;
> +		}
> +		desc->residue -= child->len;
> +	}
> +
> +	return false;
> +}
> +
>  static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
>  {
>  	dma_addr_t llp;
> @@ -354,34 +386,10 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
>  	dev_vdbg(dmaengine_chan_dev(&dwc->chan), "%s: llp=%pad\n", __func__, &llp);
>
>  	list_for_each_entry_safe(desc, _desc, &dwc->active_list, desc_node) {
> -		/* Initial residue value */
> -		desc->residue = desc->total_len;
> -
> -		/* Check first descriptors addr */
> -		if (desc->txd.phys == DWC_LLP_LOC(llp)) {
> -			spin_unlock_irqrestore(&dwc->lock, flags);
> -			return;
> -		}
> -
> -		/* Check first descriptors llp */
> -		if (lli_read(desc, llp) == llp) {
> -			/* This one is currently in progress */
> -			desc->residue -= dwc_get_sent(dwc);
> +		if (dwc_get_hard_llp_desc_residue(dwc, desc, llp)) {
>  			spin_unlock_irqrestore(&dwc->lock, flags);
>  			return;
>  		}
> -
> -		desc->residue -= desc->len;
> -		list_for_each_entry(child, &desc->tx_list, desc_node) {
> -			if (lli_read(child, llp) == llp) {
> -				/* Currently in progress */
> -				desc->residue -= dwc_get_sent(dwc);
> -				spin_unlock_irqrestore(&dwc->lock, flags);
> -				return;
> -			}
> -			desc->residue -= child->len;
> -		}
> -
>  	}
>
>  	/* Residue describes source reads; only RAW.XFER completes a transfer. */
>
> --
> 2.53.0
>