Re: [PATCH v6 4/6] dmaengine: dw-edma: Add delegated channel request helpers

[Frank Li]

On Tue, Aug 04, 2026 at 12:38:53PM +0900, Koichiro Den wrote:
> Endpoint functions that expose endpoint-local DesignWare eDMA channels
> to a remote host need to reserve exact hardware channels and hand
> interrupt ownership to the remote side before publishing the channels.
>
> Add DW eDMA-specific helpers that request a write/read hardware channel
> through DMAengine, keep the hardware-channel filter private to dw-edma,
> and switch the selected endpoint-local channel to remote interrupt
> routing after the channel has been successfully reserved. The matching
> release helper can quiesce the channel while it is still remote-routed,
> then restores the channel's default routing before releasing the
> DMAengine reservation. This lets callers skip quiesce when unwinding a
> reservation that was never exposed to host programming.
>
> Release is best-effort because its callers cannot abort teardown. Report
> a quiesce failure locally, but always restore the default routing and
> release the DMAengine reservation.
>
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> ---
> Changes in v6:
>   - No changes.
>
>  drivers/dma/dw-edma/dw-edma-core.c | 91 ++++++++++++++++++++++++++++++
>  include/linux/dma/edma.h           | 14 +++++
>  2 files changed, 105 insertions(+)
>
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index 1f893dc54c79..4c0d2bba755b 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -1302,6 +1302,97 @@ int dw_edma_remove(struct dw_edma_chip *chip)
>  }
>  EXPORT_SYMBOL_GPL(dw_edma_remove);
>
> +struct dw_edma_delegated_chan_filter_args {
> +	struct device *dma_dev;
> +	bool write;
> +	u16 id;
> +};
> +
> +static bool dw_edma_delegated_chan_filter(struct dma_chan *dchan, void *param)
> +{
> +	struct dw_edma_delegated_chan_filter_args *filter = param;
> +	struct dw_edma_chan *chan;
> +
> +	if (!filter || dchan->device->dev != filter->dma_dev)
> +		return false;
> +
> +	chan = dchan2dw_edma_chan(dchan);
> +
> +	return chan->dir == (filter->write ? EDMA_DIR_WRITE : EDMA_DIR_READ) &&
> +	       chan->id == filter->id;
> +}
> +
> +static int dw_edma_delegate_chan(struct dma_chan *dchan)
> +{
> +	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
> +	int ret = 0;
> +
> +	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
> +		return -EINVAL;
> +
> +	guard(spinlock_irqsave)(&chan->vc.lock);
> +
> +	if (chan->configured || chan->status != EDMA_ST_IDLE ||
> +	    chan->request != EDMA_REQ_NONE)
> +		ret = -EBUSY;
> +	else
> +		chan->irq_mode = DW_EDMA_CH_IRQ_REMOTE;
> +
> +	return ret;
> +}
> +
> +struct dma_chan *dw_edma_request_delegated_chan(struct device *dma_dev,
> +						bool write, u16 id)
> +{
> +	struct dw_edma_delegated_chan_filter_args filter = {
> +		.dma_dev = dma_dev,
> +		.write = write,
> +		.id = id,
> +	};
> +	struct dma_chan *dchan;
> +	dma_cap_mask_t mask;
> +
> +	if (!dma_dev)
> +		return NULL;
> +
> +	dma_cap_zero(mask);
> +	dma_cap_set(DMA_SLAVE, mask);
> +
> +	dchan = dma_request_channel(mask, dw_edma_delegated_chan_filter,
> +				    &filter);
> +	if (!dchan)
> +		return NULL;

I forget, why need export delegrated dma channel to dmanegine? If EP
driver doesn't report delegrated channel to dma engine, what's happen?

Frank

> +
> +	if (dw_edma_delegate_chan(dchan)) {
> +		dma_release_channel(dchan);
> +		return NULL;
> +	}
> +
> +	return dchan;
> +}
> +EXPORT_SYMBOL_GPL(dw_edma_request_delegated_chan);
> +
> +void dw_edma_release_delegated_chan(struct dma_chan *dchan, bool quiesce)
> +{
> +	struct dw_edma_chan *chan;
> +
> +	if (!dchan)
> +		return;
> +
> +	chan = dchan2dw_edma_chan(dchan);
> +	if (quiesce && dw_edma_core_ch_quiesce(chan))
> +		dev_warn(chan->dw->chip->dev,
> +			 "failed to quiesce delegated %s channel %u\n",
> +			 chan->dir == EDMA_DIR_WRITE ? "write" : "read",
> +			 chan->id);
> +
> +	scoped_guard(spinlock_irqsave, &chan->vc.lock)
> +		chan->irq_mode = dw_edma_get_default_irq_mode(chan);
> +
> +	dma_release_channel(dchan);
> +}
> +EXPORT_SYMBOL_GPL(dw_edma_release_delegated_chan);
> +
>  MODULE_LICENSE("GPL v2");
>  MODULE_DESCRIPTION("Synopsys DesignWare eDMA controller core driver");
>  MODULE_AUTHOR("Gustavo Pimentel <gustavo.pimentel@xxxxxxxxxxxx>");
> diff --git a/include/linux/dma/edma.h b/include/linux/dma/edma.h
> index 3c8e2ef9dee0..944469258b8b 100644
> --- a/include/linux/dma/edma.h
> +++ b/include/linux/dma/edma.h
> @@ -153,6 +153,9 @@ struct dw_edma_chip {
>  #if IS_REACHABLE(CONFIG_DW_EDMA)
>  int dw_edma_probe(struct dw_edma_chip *chip);
>  int dw_edma_remove(struct dw_edma_chip *chip);
> +struct dma_chan *dw_edma_request_delegated_chan(struct device *dma_dev,
> +						bool write, u16 id);
> +void dw_edma_release_delegated_chan(struct dma_chan *chan, bool quiesce);
>  #else
>  static inline int dw_edma_probe(struct dw_edma_chip *chip)
>  {
> @@ -163,6 +166,17 @@ static inline int dw_edma_remove(struct dw_edma_chip *chip)
>  {
>  	return 0;
>  }
> +
> +static inline struct dma_chan *
> +dw_edma_request_delegated_chan(struct device *dma_dev, bool write, u16 id)
> +{
> +	return NULL;
> +}
> +
> +static inline void dw_edma_release_delegated_chan(struct dma_chan *chan,
> +						  bool quiesce)
> +{
> +}
>  #endif /* CONFIG_DW_EDMA */
>
>  #endif /* _DW_EDMA_H */
> --
> 2.51.0
>