Re: [PATCH v3 2/3] dmaengine: dw-edma: Configure remote interrupt routing

[Koichiro Den]

On Fri, Sep 04, 2026 at 10:41:47AM -0500, Frank Li wrote:
> On Thu, Sep 03, 2026 at 03:45:32PM +0900, Koichiro Den wrote:
> > An endpoint function can reserve an endpoint-local channel while the RC
> > programs it through an exposed register window. Such a channel must route
> > interrupts remotely and ignore them on the endpoint.
> >
> > Use dma_slave_config to set per-channel interrupt routing on idle channels
> > of a local eDMA-compatible instance. Releasing a remote-routed channel
> > quiesces the hardware and drains its local IRQ before restoring the default
> > routing.
> >
> > The eDMA quiesce may stop a complete direction. The caller must own every
> > channel in that direction and stop remote programming first.
> >
> > Suggested-by: Frank Li <Frank.Li@xxxxxxx>
> > Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> > ---
> > Changes in v3:
> >   - Add struct dw_edma_chan_config with validity flags for non-LL mode and
> >     interrupt routing. (Frank)
> >     https://lore.kernel.org/r/apWj7zzAw57U2r4F@SMW015318/
> >   - Do not skip generic dma_slave_config fields when private settings are
> >     supplied. (Sashiko)
> >     https://lore.kernel.org/r/20260828164950.61AE51F000E9@xxxxxxxxxxxxxxx/
> >   - Use READ_ONCE()/WRITE_ONCE() for IRQ mode accessed by shared handlers
> >     and drain the channel IRQ before restoring local routing. (Sashiko)
> >
> >  drivers/dma/dw-edma/dw-edma-core.c | 135 ++++++++++++++++++++++-------
> >  drivers/dma/dw-edma/dw-edma-core.h |   5 +-
> >  include/linux/dma/edma.h           |  19 ++++
> >  3 files changed, 126 insertions(+), 33 deletions(-)
> >
> > diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> > index a678c70a78fe..e3786d960a43 100644
> > --- a/drivers/dma/dw-edma/dw-edma-core.c
> > +++ b/drivers/dma/dw-edma/dw-edma-core.c
> > @@ -177,48 +177,79 @@ dw_edma_get_default_irq_mode(struct dw_edma_chan *chan)
> >  						  DW_EDMA_CH_IRQ_REMOTE;
> >  }
> >
> > +static int dw_edma_device_config_irq_mode(struct dw_edma_chan *chan,
> > +					  enum dw_edma_ch_irq_mode mode)
> > +{
> > +	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL) ||
> > +	    (mode != DW_EDMA_CH_IRQ_LOCAL && mode != DW_EDMA_CH_IRQ_REMOTE))
> > +		return -EINVAL;
> > +
> > +	guard(spinlock_irqsave)(&chan->vc.lock);
> > +
> > +	if (chan->configured || chan->status != EDMA_ST_IDLE ||
> > +	    chan->request != EDMA_REQ_NONE)
> > +		return -EBUSY;
> > +
> > +	WRITE_ONCE(chan->irq_mode, mode);
> > +
> > +	return 0;
> > +}
> > +
> >  static int dw_edma_device_config(struct dma_chan *dchan,
> >  				 struct dma_slave_config *config)
> >  {
> > +	const struct dw_edma_chan_config *dw_config = config->peripheral_config;
> >  	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
> > -	bool cfg_non_ll;
> > -	int non_ll = 0;
> > -
> > -	chan->non_ll = false;
> > -	if (chan->dw->chip->mf == EDMA_MF_HDMA_NATIVE) {
> > -		if (config->peripheral_config &&
> > -		    config->peripheral_size != sizeof(int)) {
> > -			dev_err(dchan->device->dev,
> > -				"config param peripheral size mismatch\n");
> > +	bool non_ll = false;
> > +	u32 flags = 0;
> > +	int ret;
> > +
> > +	if (dw_config) {
> > +		if (config->peripheral_size != sizeof(*dw_config) ||
> > +		    dw_config->flags & ~(DW_EDMA_CH_CONFIG_NON_LL |
> > +					 DW_EDMA_CH_CONFIG_IRQ_MODE))
> > +			return -EINVAL;
> > +		flags = dw_config->flags;
> > +	}
> > +
> > +	/*
> > +	 * When there is no valid LLP base address available then the
> > +	 * default DMA ops will use the non-LL mode.
> > +	 *
> > +	 * When LL mode is the default, clients can request non-LL mode
> > +	 * through DW_EDMA_CH_CONFIG_NON_LL.
> > +	 */
> > +	non_ll = chan->dw->chip->mf == EDMA_MF_HDMA_NATIVE &&
> > +		 chan->dw->chip->cfg_non_ll;
> > +
> > +	if (flags & DW_EDMA_CH_CONFIG_NON_LL) {
> > +		if (chan->dw->chip->mf != EDMA_MF_HDMA_NATIVE)
> > +			return -EINVAL;
> > +
> > +		if (chan->dw->chip->cfg_non_ll && !dw_config->non_ll) {
> > +			dev_err(dchan->device->dev, "invalid configuration\n");
> >  			return -EINVAL;
> >  		}
> >
> > -		/*
> > -		 * When there is no valid LLP base address available then the
> > -		 * default DMA ops will use the non-LL mode.
> > -		 *
> > -		 * Cases where LL mode is enabled and client wants to use the
> > -		 * non-LL mode then also client can do so via providing the
> > -		 * peripheral_config param.
> > -		 */
> > -		cfg_non_ll = chan->dw->chip->cfg_non_ll;
> > -		if (config->peripheral_config) {
> > -			non_ll = *(int *)config->peripheral_config;
> > +		non_ll = dw_config->non_ll;
> > +	}
> >
> > -			if (cfg_non_ll && !non_ll) {
> > -				dev_err(dchan->device->dev, "invalid configuration\n");
> > -				return -EINVAL;
> > -			}
> > +	if (flags & DW_EDMA_CH_CONFIG_IRQ_MODE) {
> > +		switch (chan->dw->chip->mf) {
> > +		case EDMA_MF_EDMA_LEGACY:
> > +		case EDMA_MF_EDMA_UNROLL:
> > +		case EDMA_MF_HDMA_COMPAT:
> > +			break;
> > +		default:
> > +			return -EINVAL;
> >  		}
> >
> > -		if (cfg_non_ll || non_ll)
> > -			chan->non_ll = true;
> > -	} else if (config->peripheral_config) {
> > -		dev_err(dchan->device->dev,
> > -			"peripheral config param applicable only for HDMA\n");
> > -		return -EINVAL;
> > +		ret = dw_edma_device_config_irq_mode(chan, dw_config->irq_mode);
> > +		if (ret)
> > +			return ret;
> >  	}
> >
> > +	chan->non_ll = non_ll;
> >  	memcpy(&chan->config, config, sizeof(*config));
> >  	chan->configured = true;
> >
> > @@ -890,11 +921,48 @@ static void dw_edma_wait_termination(struct dma_chan *dchan)
> >  		 "timeout waiting for channel termination\n");
> >  }
> >
> > +static void dw_edma_synchronize_chan_irq(struct dw_edma_chan *chan)
> > +{
> > +	struct dw_edma *dw = chan->dw;
> > +	unsigned long *mask;
> > +	int i;
> > +
> > +	/*
> > +	 * With nr_irqs == 1, the common handler can enter for the other direction
> > +	 * and retain a status snapshot for the remotely owned direction across
> > +	 * quiesce. With multiple IRQs, the handler covering this channel can likewise
> > +	 * enter for another IRQ sharer. Drain the IRQ whose mask contains the channel
> > +	 * before restoring local routing.
> > +	 */
> > +	for (i = 0; i < dw->nr_irqs; i++) {
> > +		mask = chan->dir == EDMA_DIR_WRITE ? dw->irq[i].wr_mask :
> > +						     dw->irq[i].rd_mask;
> > +		if (!test_bit(chan->id, mask))
> > +			continue;
> > +
> > +		synchronize_irq(dw->chip->ops->irq_vector(dw->chip->dev, i));
> > +		return;
> > +	}
> > +}
> > +
> >  static void dw_edma_device_synchronize(struct dma_chan *dchan)
> >  {
> >  	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
> > +	bool remote;
> > +
> > +	scoped_guard(spinlock_irqsave, &chan->vc.lock)
> > +		remote = chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL &&
> > +			 chan->irq_mode == DW_EDMA_CH_IRQ_REMOTE;
> > +
> > +	if (remote && dw_edma_core_ch_quiesce(chan))
> > +		dev_warn(chan->dw->chip->dev,
> > +			 "failed to quiesce remote-routed %s channel %u\n",
> > +			 chan->dir == EDMA_DIR_WRITE ? "write" : "read",
> > +			 chan->id);
> >
> >  	dw_edma_wait_termination(dchan);
> > +	if (remote)
> > +		dw_edma_synchronize_chan_irq(chan);
> >  	cancel_work_sync(&chan->irq_work);
> >  	atomic_set(&chan->irq_pending, 0);
> >  	vchan_synchronize(&chan->vc);
> > @@ -903,12 +971,17 @@ static void dw_edma_device_synchronize(struct dma_chan *dchan)
> >  static void dw_edma_free_chan_resources(struct dma_chan *dchan)
> >  {
> >  	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
> > +	enum dw_edma_ch_irq_mode default_mode =
> > +			dw_edma_get_default_irq_mode(chan);
> >
> >  	dw_edma_device_terminate_all(dchan);
> >  	dw_edma_device_synchronize(dchan);
> >
> > -	scoped_guard(spinlock_irqsave, &chan->vc.lock)
> > +	scoped_guard(spinlock_irqsave, &chan->vc.lock) {
> >  		chan->configured = false;
> > +		if (chan->irq_mode != default_mode)
> > +			WRITE_ONCE(chan->irq_mode, default_mode);
> > +	}
> >
> >  	vchan_free_chan_resources(&chan->vc);
> >  }
> > diff --git a/drivers/dma/dw-edma/dw-edma-core.h b/drivers/dma/dw-edma/dw-edma-core.h
> > index f6a5ad317567..275d362d1805 100644
> > --- a/drivers/dma/dw-edma/dw-edma-core.h
> > +++ b/drivers/dma/dw-edma/dw-edma-core.h
> > @@ -280,11 +280,12 @@ static inline bool
> >  dw_edma_core_ch_ignore_irq(struct dw_edma_chan *chan)
> >  {
> >  	struct dw_edma *dw = chan->dw;
> > +	enum dw_edma_ch_irq_mode mode = READ_ONCE(chan->irq_mode);
> >
> >  	if (dw->chip->flags & DW_EDMA_CHIP_LOCAL)
> > -		return chan->irq_mode == DW_EDMA_CH_IRQ_REMOTE;
> > +		return mode == DW_EDMA_CH_IRQ_REMOTE;
> >  	else
> > -		return chan->irq_mode == DW_EDMA_CH_IRQ_LOCAL;
> > +		return mode == DW_EDMA_CH_IRQ_LOCAL;
> >  }
> 
> does this tunk fix something, you make this change later.

I added this for a possible race with the shared IRQ handler, especially when
nr_irqs == 1.

... but after carefully thinking about this again, the hunk seems unnecessary.

- Before undelegating (changing the irq_mode from REMOTE to LOCAL), the client
  must stop remote programming, and the driver quiesces the direction and
  synchronizes the local IRQ.
  At that point, no-one is supposed to issue any transfer for the channel
- Conversely, remote routing is configured while the channel is idle, before the
  peer starts programming it.

If the peer continued programming during either transition, it just breaks
things. READ_ONCE()/WRITE_ONCE() would not make the handoff safe.

I will drop this hunk and the corresponding WRITE_ONCE() use.

> 
> >
> >  #endif /* _DW_EDMA_CORE_H */
> > diff --git a/include/linux/dma/edma.h b/include/linux/dma/edma.h
> > index 3c8e2ef9dee0..93f866d57987 100644
> > --- a/include/linux/dma/edma.h
> > +++ b/include/linux/dma/edma.h
> > @@ -101,6 +101,25 @@ enum dw_edma_ch_irq_mode {
> >  	DW_EDMA_CH_IRQ_REMOTE,
> >  };
> >
> > +#define DW_EDMA_CH_CONFIG_NON_LL	BIT(0)
> 
> you need update other non_ll user to set DW_EDMA_CH_CONFIG_NON_LL.

Ugh, I missed updating the existing non-LL user. I will respin.

Thanks for the review.

Best regards,
Koichiro

> 
> Frank
> 
> > +#define DW_EDMA_CH_CONFIG_IRQ_MODE	BIT(1)
> > +
> > +/**
> > + * struct dw_edma_chan_config - dw-edma channel configuration
> > + * @flags: fields selected by DW_EDMA_CH_CONFIG_*
> > + * @non_ll: use HDMA non-linked-list mode
> > + * @irq_mode: interrupt routing mode
> > + *
> > + * Pass this structure through dma_slave_config.peripheral_config. Before
> > + * synchronizing a remote-routed channel, the client must stop remote
> > + * programming and own every channel affected by the hardware quiesce.
> > + */
> > +struct dw_edma_chan_config {
> > +	u32 flags;
> > +	bool non_ll;
> > +	enum dw_edma_ch_irq_mode irq_mode;
> > +};
> > +
> >  /**
> >   * struct dw_edma_chip - representation of DesignWare eDMA controller hardware
> >   * @dev:		 struct device of the eDMA controller
> > --
> > 2.51.0
> >