linux-kernel - Re: [RFC PATCH v4 05/38] dmaengine: dw-edma: Add a helper to query linked-list region

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Message-ID: <aW0S60D2uALBXdtQ@lizhi-Precision-Tower-5810>
Date: Sun, 18 Jan 2026 12:05:47 -0500
From: Frank Li <Frank.li@....com>
To: Koichiro Den <den@...inux.co.jp>
Cc: dave.jiang@...el.com, cassel@...nel.org, mani@...nel.org,
	kwilczynski@...nel.org, kishon@...nel.org, bhelgaas@...gle.com,
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Subject: Re: [RFC PATCH v4 05/38] dmaengine: dw-edma: Add a helper to query
 linked-list region

On Sun, Jan 18, 2026 at 10:54:07PM +0900, Koichiro Den wrote:
> A remote eDMA provider may need to expose the linked-list (LL) memory
> region that was configured by platform glue (typically at boot), so the
> peer (host) can map it and operate the remote view of the controller.
>
> Export dw_edma_chan_get_ll_region() to return the LL region associated
> with a given dma_chan.

This informaiton passed from dwc epc driver. Is it possible to get it from
EPC driver.

Frank
>
> Signed-off-by: Koichiro Den <den@...inux.co.jp>
> ---
>  drivers/dma/dw-edma/dw-edma-core.c | 26 ++++++++++++++++++++++++++
>  include/linux/dma/edma.h           | 14 ++++++++++++++
>  2 files changed, 40 insertions(+)
>
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index 0eb8fc1dcc34..c4fb66a9b5f5 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -1209,6 +1209,32 @@ int dw_edma_chan_register_notify(struct dma_chan *dchan,
>  }
>  EXPORT_SYMBOL_GPL(dw_edma_chan_register_notify);
>
> +int dw_edma_chan_get_ll_region(struct dma_chan *dchan,
> +			       struct dw_edma_region *region)
> +{
> +	struct dw_edma_chip *chip;
> +	struct dw_edma_chan *chan;
> +
> +	if (!dchan || !region || !dchan->device)
> +		return -ENODEV;
> +
> +	chan = dchan2dw_edma_chan(dchan);
> +	if (!chan)
> +		return -ENODEV;
> +
> +	chip = chan->dw->chip;
> +	if (!(chip->flags & DW_EDMA_CHIP_LOCAL))
> +		return -EINVAL;
> +
> +	if (chan->dir == EDMA_DIR_WRITE)
> +		*region = chip->ll_region_wr[chan->id];
> +	else
> +		*region = chip->ll_region_rd[chan->id];
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(dw_edma_chan_get_ll_region);
> +
>  MODULE_LICENSE("GPL v2");
>  MODULE_DESCRIPTION("Synopsys DesignWare eDMA controller core driver");
>  MODULE_AUTHOR("Gustavo Pimentel <gustavo.pimentel@...opsys.com>");
> diff --git a/include/linux/dma/edma.h b/include/linux/dma/edma.h
> index 3c538246de07..c9ec426e27ec 100644
> --- a/include/linux/dma/edma.h
> +++ b/include/linux/dma/edma.h
> @@ -153,6 +153,14 @@ bool dw_edma_chan_ignore_irq(struct dma_chan *chan);
>  int dw_edma_chan_register_notify(struct dma_chan *chan,
>  				 void (*cb)(struct dma_chan *chan, void *user),
>  				 void *user);
> +
> +/**
> + * dw_edma_chan_get_ll_region - get linked list (LL) memory for a dma_chan
> + * @chan: the target DMA channel
> + * @region: output parameter returning the corresponding LL region
> + */
> +int dw_edma_chan_get_ll_region(struct dma_chan *chan,
> +			       struct dw_edma_region *region);
>  #else
>  static inline int dw_edma_probe(struct dw_edma_chip *chip)
>  {
> @@ -182,6 +190,12 @@ static inline int dw_edma_chan_register_notify(struct dma_chan *chan,
>  {
>  	return -ENODEV;
>  }
> +
> +static inline int dw_edma_chan_get_ll_region(struct dma_chan *chan,
> +					     struct dw_edma_region *region)
> +{
> +	return -EINVAL;
> +}
>  #endif /* CONFIG_DW_EDMA */
>
>  struct pci_epc;
> --
> 2.51.0
>