Re: [PATCH v2 08/19] dmaengine: dw-edma: Centralize LL doorbell decisions

[Frank Li]

On Thu, Jul 23, 2026 at 05:41:39PM +0900, Koichiro Den wrote:
> LL fill currently rings the doorbell every time. A running eDMA or HDMA
> channel follows entries whose CB matches CCS without another kick. A
> channel stopped at a CB mismatch needs one.
>
> Move that decision to dw_edma_core_ch_maybe_doorbell(). It rings only for
> a BUSY LL channel with pending entries, no EDMA_REQ_STOP or
> EDMA_REQ_PAUSE, and hardware that is not running. The BUSY check prevents
> EDMA_REQ_STOP completion from restarting terminated work.
>
> issue_pending() still publishes LL entries only from IDLE. A later patch
> allows live appends. Non-LL channels are unchanged.
>
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> ---
> Changes in v2:
>   - New patch.
>
>  drivers/dma/dw-edma/dw-edma-core.c | 28 ++++++++++++++++++++++++++--
>  1 file changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index fa104af4146e..e88bfb417ad4 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -129,6 +129,11 @@ static bool dw_edma_core_enable_ll_irq(struct dw_edma_desc *desc, u32 i,
>  	return desc->chan->dw->core->ll_irq(desc, i, free);
>  }
>
> +static bool dw_edma_ll_pending(struct dw_edma_chan *chan)
> +{
> +	return chan->ll_head != chan->ll_end;
> +}
> +
>  static void dw_edma_core_ll_start(struct dw_edma_desc *desc)
>  {
>  	struct dw_edma_chan *chan = desc->chan;
> @@ -163,8 +168,6 @@ static void dw_edma_core_ll_start(struct dw_edma_desc *desc)
>
>  	desc->done_burst = desc->start_burst;
>  	desc->start_burst = i;
> -
> -	dw_edma_core_ch_doorbell(chan);
>  }
>
>  static void dw_edma_core_start(struct dw_edma_desc *desc)
> @@ -232,6 +235,23 @@ static void dw_edma_terminate_all_descs(struct dw_edma_chan *chan)
>  	dw_edma_terminate_vdesc_list(&chan->vc.desc_submitted);
>  }
>
> +/* Must be called with vc.lock held. */
> +static void dw_edma_core_ch_maybe_doorbell(struct dw_edma_chan *chan)

suggest this function call dw_edma_core_ch_doorbell()

old dw_edma_core_ch_doorbell() rename to dw_edma_core_do_ch_doorbell()

Frank

> +{
> +	if (chan->non_ll || chan->request != EDMA_REQ_NONE ||
> +	    chan->status != EDMA_ST_BUSY || !dw_edma_ll_pending(chan))
> +		return;
> +
> +	/*
> +	 * While running, both legacy eDMA and HDMA consume newly published
> +	 * elements without another doorbell.
> +	 */
> +	if (dw_edma_core_ch_status(chan) == DMA_IN_PROGRESS)
> +		return;
> +
> +	dw_edma_core_ch_doorbell(chan);
> +}
> +
>  static void dw_edma_device_caps(struct dma_chan *dchan,
>  				struct dma_slave_caps *caps)
>  {
> @@ -357,6 +377,7 @@ static int dw_edma_device_resume(struct dma_chan *dchan)
>  		chan->status = EDMA_ST_BUSY;
>  		if (!dw_edma_start_transfer(chan))
>  			chan->status = EDMA_ST_IDLE;
> +		dw_edma_core_ch_maybe_doorbell(chan);
>  	}
>
>  	return err;
> @@ -405,6 +426,7 @@ static void dw_edma_device_issue_pending(struct dma_chan *dchan)
>  	    chan->status == EDMA_ST_IDLE) {
>  		chan->status = EDMA_ST_BUSY;
>  		dw_edma_start_transfer(chan);
> +		dw_edma_core_ch_maybe_doorbell(chan);
>  	}
>  	spin_unlock_irqrestore(&chan->vc.lock, flags);
>  }
> @@ -720,6 +742,8 @@ static void dw_edma_done_interrupt(struct dw_edma_chan *chan)
>  	default:
>  		break;
>  	}
> +	dw_edma_core_ch_maybe_doorbell(chan);
> +
>  	spin_unlock_irqrestore(&chan->vc.lock, flags);
>  }
>
> --
> 2.51.0
>