Re: [PATCH v5 01/24] dmaengine: dw-edma: Add dw_edma_core_ll_cur_idx() to get current LL entry index

On Thu, Aug 13, 2026 at 12:56:58AM +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]>
> Reviewed-by: Frank Li <[email protected]>
> Co-developed-by: Koichiro Den <[email protected]>
> Signed-off-by: Koichiro Den <[email protected]>
> ---
> Changes in v5:
>   - Reject an all-ones DMA_LLP value before converting it to an LL
>     index. (Sashiko)
>
> @Frank, I kept your R-b tag since the v5 change is only a small validation
> check. Please let me know if you prefer me to drop it.

look good

Frank
>
>  drivers/dma/dw-edma/dw-edma-core.h    | 10 ++++++++++
>  drivers/dma/dw-edma/dw-edma-v0-core.c | 20 ++++++++++++++++++++
>  drivers/dma/dw-edma/dw-hdma-v0-core.c | 20 ++++++++++++++++++++
>  include/linux/dma/edma.h              |  2 +-
>  4 files changed, 51 insertions(+), 1 deletion(-)
>
> 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..cc8059182940 100644
> --- a/drivers/dma/dw-edma/dw-edma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-v0-core.c
> @@ -616,6 +616,25 @@ 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));
> +
> +	/*
> +	 * LL regions stay within one 4 GiB address window. Reject an all-ones
> +	 * MMIO value. If the low word is zero, use the high word to distinguish
> +	 * a nonzero boundary address from an unprogrammed all-zero context.
> +	 */
> +	if (val == U32_MAX ||
> +	    (!val && !GET_CH_32(chan->dw, chan->dir, chan->id, llp.msb)))
> +		return -EINVAL;
> +
> +	return (val - base) / EDMA_LL_SZ;
> +}
> +
>  /* eDMA debugfs callbacks */
>  static void dw_edma_v0_core_debugfs_on(struct dw_edma *dw)
>  {
> @@ -650,6 +669,7 @@ 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..19da1c8fd615 100644
> --- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> @@ -384,6 +384,25 @@ 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));
> +
> +	/*
> +	 * LL regions stay within one 4 GiB address window. Reject an all-ones
> +	 * MMIO value. If the low word is zero, use the high word to distinguish
> +	 * a nonzero boundary address from an unprogrammed all-zero context.
> +	 */
> +	if (val == U32_MAX ||
> +	    (!val && !GET_CH_32(chan->dw, chan->dir, chan->id, llp.msb)))
> +		return -EINVAL;
> +
> +	return (val - base) / EDMA_LL_SZ;
> +}
> +
>  /* HDMA debugfs callbacks */
>  static void dw_hdma_v0_core_debugfs_on(struct dw_edma *dw)
>  {
> @@ -406,6 +425,7 @@ 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,
> diff --git a/include/linux/dma/edma.h b/include/linux/dma/edma.h
> index 3c8e2ef9dee0..a4e5aab8fddc 100644
> --- a/include/linux/dma/edma.h
> +++ b/include/linux/dma/edma.h
> @@ -130,7 +130,7 @@ struct dw_edma_chip {
>
>  	u16			ll_wr_cnt;
>  	u16			ll_rd_cnt;
> -	/* link list address */
> +	/* Linked-list regions must not cross a 4 GiB address boundary. */
>  	struct dw_edma_region	ll_region_wr[HDMA_MAX_WR_CH];
>  	struct dw_edma_region	ll_region_rd[HDMA_MAX_RD_CH];
>
> --
> 2.51.0
>