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

On Tue, Aug 04, 2026 at 11:23:47AM -0500, Frank Li wrote:
> 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 <[email protected]>
> > ---
> > 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?

This just reserves the exact channel against any dmaengine clients before
handing its programming ownership to the host. Without it, a local client
could request the same channel too.

Best regards,
Koichiro

> 
> 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 <[email protected]>");
> > 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
> >