Re: [PATCH v2 01/19] dmaengine: dw-edma: Add dw_edma_core_ll_cur_idx() to get current LL entry index

On Thu, Jul 23, 2026 at 05:41:32PM +0900, Koichiro Den wrote:
> From: Frank Li <[email protected]>
>
> Add dw_edma_core_ll_cur_idx() to get the current LL entry index and
> prepare for dynamic addition of DMA requests while the DMA engine is
> running.
>
> Signed-off-by: Frank Li <[email protected]>
> Co-developed-by: Koichiro Den <[email protected]>
> Signed-off-by: Koichiro Den <[email protected]>
> ---

Reviewed-by: Frank Li <[email protected]>

> Based on Frank's original submission:
> https://lore.kernel.org/dmaengine/[email protected]/
>
> Changes in v2:
>   - Handle zero low words and low-word wrap without reading DMA_LLP.MSB
>     on the normal path, and clarify the lost-context comments.
>
>  drivers/dma/dw-edma/dw-edma-core.h    | 10 ++++++++++
>  drivers/dma/dw-edma/dw-edma-v0-core.c | 19 +++++++++++++++++++
>  drivers/dma/dw-edma/dw-hdma-v0-core.c | 19 +++++++++++++++++++
>  3 files changed, 48 insertions(+)
>
> diff --git a/drivers/dma/dw-edma/dw-edma-core.h b/drivers/dma/dw-edma/dw-edma-core.h
> index f6a5ad317567..e50fa7965778 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.h
> +++ b/drivers/dma/dw-edma/dw-edma-core.h
> @@ -138,6 +138,7 @@ struct dw_edma_core_ops {
>  	void (*ll_data)(struct dw_edma_chan *chan, struct dw_edma_burst *burst,
>  			u32 idx, bool cb, bool irq);
>  	void (*ll_link)(struct dw_edma_chan *chan, u32 idx, bool cb, u64 addr);
> +	int (*ll_cur_idx)(struct dw_edma_chan *chan);
>  	void (*ch_doorbell)(struct dw_edma_chan *chan);
>  	void (*ch_enable)(struct dw_edma_chan *chan);
>  	void (*ch_config)(struct dw_edma_chan *chan);
> @@ -181,6 +182,15 @@ struct dw_edma_chan *dchan2dw_edma_chan(struct dma_chan *dchan)
>  	return vc2dw_edma_chan(to_virt_chan(dchan));
>  }
>
> +/*
> + * Return the current LL entry index. A negative value means that the channel
> + * context is not initialized or was lost after a link reset.
> + */
> +static inline int dw_edma_core_ll_cur_idx(struct dw_edma_chan *chan)
> +{
> +	return chan->dw->core->ll_cur_idx(chan);
> +}
> +
>  static inline u64 dw_edma_core_get_ll_paddr(struct dw_edma_chan *chan)
>  {
>  	if (chan->dir == EDMA_DIR_WRITE)
> diff --git a/drivers/dma/dw-edma/dw-edma-v0-core.c b/drivers/dma/dw-edma/dw-edma-v0-core.c
> index abc1bd4c0be2..ba84811234e1 100644
> --- a/drivers/dma/dw-edma/dw-edma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-v0-core.c
> @@ -616,6 +616,24 @@ static void dw_edma_v0_core_ch_doorbell(struct dw_edma_chan *chan)
>  		  FIELD_PREP(EDMA_V0_DOORBELL_CH_MASK, chan->id));
>  }
>
> +static int dw_edma_v0_core_ll_cur_idx(struct dw_edma_chan *chan)
> +{
> +	u32 base, val;
> +
> +	val = GET_CH_32(chan->dw, chan->dir, chan->id, llp.lsb);
> +	base = lower_32_bits(dw_edma_core_get_ll_paddr(chan));
> +
> +	/*
> +	 * An all-zero pointer means that the channel context is unavailable,
> +	 * so an LL region starting at DMA address zero is not supported.
> +	 */
> +	if (!val && !GET_CH_32(chan->dw, chan->dir, chan->id, llp.msb))
> +		return -EINVAL;
> +
> +	/* u32 subtraction handles a low-word wrap at a 4 GiB boundary. */
> +	return (val - base) / EDMA_LL_SZ;
> +}
> +
>  /* eDMA debugfs callbacks */
>  static void dw_edma_v0_core_debugfs_on(struct dw_edma *dw)
>  {
> @@ -650,6 +668,7 @@ static const struct dw_edma_core_ops dw_edma_v0_core = {
>  	.handle_int = dw_edma_v0_core_handle_int,
>  	.ll_data = dw_edma_v0_core_ll_data,
>  	.ll_link = dw_edma_v0_core_ll_link,
> +	.ll_cur_idx = dw_edma_v0_core_ll_cur_idx,
>  	.ch_doorbell = dw_edma_v0_core_ch_doorbell,
>  	.ch_enable = dw_edma_v0_core_ch_enable,
>  	.ch_config = dw_edma_v0_core_ch_config,
> diff --git a/drivers/dma/dw-edma/dw-hdma-v0-core.c b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> index 36ee72efcd31..2fc7f8e85b43 100644
> --- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> @@ -384,6 +384,24 @@ static void dw_hdma_v0_core_ch_doorbell(struct dw_edma_chan *chan)
>  	SET_CH_32(dw, chan->dir, chan->id, doorbell, HDMA_V0_DOORBELL_START);
>  }
>
> +static int dw_hdma_v0_core_ll_cur_idx(struct dw_edma_chan *chan)
> +{
> +	u32 base, val;
> +
> +	val = GET_CH_32(chan->dw, chan->dir, chan->id, llp.lsb);
> +	base = lower_32_bits(dw_edma_core_get_ll_paddr(chan));
> +
> +	/*
> +	 * An all-zero pointer means that the channel context is unavailable,
> +	 * so an LL region starting at DMA address zero is not supported.
> +	 */
> +	if (!val && !GET_CH_32(chan->dw, chan->dir, chan->id, llp.msb))
> +		return -EINVAL;
> +
> +	/* u32 subtraction handles a low-word wrap at a 4 GiB boundary. */
> +	return (val - base) / EDMA_LL_SZ;
> +}
> +
>  /* HDMA debugfs callbacks */
>  static void dw_hdma_v0_core_debugfs_on(struct dw_edma *dw)
>  {
> @@ -406,6 +424,7 @@ static const struct dw_edma_core_ops dw_hdma_v0_core = {
>  	.non_ll_start = dw_hdma_v0_core_non_ll_start,
>  	.ll_data = dw_hdma_v0_core_ll_data,
>  	.ll_link = dw_hdma_v0_core_ll_link,
> +	.ll_cur_idx = dw_hdma_v0_core_ll_cur_idx,
>  	.ch_doorbell = dw_hdma_v0_core_ch_doorbell,
>  	.ch_enable = dw_hdma_v0_core_ch_enable,
>  	.ch_config = dw_hdma_v0_core_ch_config,
> --
> 2.51.0
>