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.

Signed-off-by: Koichiro Den <den@valinux.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@synopsys.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

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@valinux.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@synopsys.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
>

On Sun, Jan 18, 2026 at 12:05:47PM -0500, Frank Li wrote:
> 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.

That makes sense, from an API cleanness perspective, thanks.
I'll add a helper function dw_pcie_edma_get_ll_region() in
drivers/pci/controller/dwc/pcie-designware.c, instead of the current
dw_edma_chan_get_ll_region() in dw-edma-core.c.

Thanks for the review,
Koichiro

> 
> Frank
> >
> > Signed-off-by: Koichiro Den <den@valinux.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@synopsys.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
> >

On Wed, Jan 21, 2026 at 10:38:53AM +0900, Koichiro Den wrote:
> On Sun, Jan 18, 2026 at 12:05:47PM -0500, Frank Li wrote:
> > 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.
> 
> That makes sense, from an API cleanness perspective, thanks.
> I'll add a helper function dw_pcie_edma_get_ll_region() in
> drivers/pci/controller/dwc/pcie-designware.c, instead of the current
> dw_edma_chan_get_ll_region() in dw-edma-core.c.

Hi Frank,

I looked into exposing LL regions from the EPC driver side, but the key
issue is channel identification under possibly concurrent dmaengine users.
In practice, the only stable handle a consumer has is a pointer to struct
dma_chan, and the only reliable way to map that to the eDMA hardware
channel is via dw_edma_chan->id. I think an EPC-facing API would still need
that mapping in any case, so keeping the helper in dw-edma seems simpler
and more robust.
If you have another idea, I'd appreciate your insights.

Regards,
Koichiro

> 
> Thanks for the review,
> Koichiro
> 
> > 
> > Frank
> > >
> > > Signed-off-by: Koichiro Den <den@valinux.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@synopsys.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
> > >

On Wed, Jan 21, 2026 at 05:41:11PM +0900, Koichiro Den wrote:
> On Wed, Jan 21, 2026 at 10:38:53AM +0900, Koichiro Den wrote:
> > On Sun, Jan 18, 2026 at 12:05:47PM -0500, Frank Li wrote:
> > > 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.
> >
> > That makes sense, from an API cleanness perspective, thanks.
> > I'll add a helper function dw_pcie_edma_get_ll_region() in
> > drivers/pci/controller/dwc/pcie-designware.c, instead of the current
> > dw_edma_chan_get_ll_region() in dw-edma-core.c.
>
> Hi Frank,
>
> I looked into exposing LL regions from the EPC driver side, but the key
> issue is channel identification under possibly concurrent dmaengine users.
> In practice, the only stable handle a consumer has is a pointer to struct
> dma_chan, and the only reliable way to map that to the eDMA hardware
> channel is via dw_edma_chan->id.

If possible, I suggest change to one page pre-channel. So there are a fixed
ll mapping.

> I think an EPC-facing API would still need
> that mapping in any case, so keeping the helper in dw-edma seems simpler
> and more robust.
> If you have another idea, I'd appreciate your insights.

I suggest add generally DMA engine API to get such property, some likes
a kind ioctrl \ dma_get_config().

Frank

>
> Regards,
> Koichiro
>
> >
> > Thanks for the review,
> > Koichiro
> >
> > >
> > > Frank
> > > >
> > > > Signed-off-by: Koichiro Den <den@valinux.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@synopsys.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
> > > >

On Wed, Jan 21, 2026 at 10:24:01AM -0500, Frank Li wrote:
> On Wed, Jan 21, 2026 at 05:41:11PM +0900, Koichiro Den wrote:
> > On Wed, Jan 21, 2026 at 10:38:53AM +0900, Koichiro Den wrote:
> > > On Sun, Jan 18, 2026 at 12:05:47PM -0500, Frank Li wrote:
> > > > 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.
> > >
> > > That makes sense, from an API cleanness perspective, thanks.
> > > I'll add a helper function dw_pcie_edma_get_ll_region() in
> > > drivers/pci/controller/dwc/pcie-designware.c, instead of the current
> > > dw_edma_chan_get_ll_region() in dw-edma-core.c.
> >
> > Hi Frank,
> >
> > I looked into exposing LL regions from the EPC driver side, but the key
> > issue is channel identification under possibly concurrent dmaengine users.
> > In practice, the only stable handle a consumer has is a pointer to struct
> > dma_chan, and the only reliable way to map that to the eDMA hardware
> > channel is via dw_edma_chan->id.
> 
> If possible, I suggest change to one page pre-channel. So there are a fixed
> ll mapping.

I agree that this would make the LL layout more deterministic and would
indeed simplify locating the region for a given dw_edma_chan ID. That said,
my concern was that even with a fixed per-channel layout, we still need a
reliable way to map a struct dma_chan obtained by a consumer to the
corresponding dw_edma_chan ID, especially in the presence of potentially
concurrent dmaengine users.

> 
> > I think an EPC-facing API would still need
> > that mapping in any case, so keeping the helper in dw-edma seems simpler
> > and more robust.
> > If you have another idea, I'd appreciate your insights.
> 
> I suggest add generally DMA engine API to get such property, some likes
> a kind ioctrl \ dma_get_config().

I think such a helper, combined with your one page per-channel idea, would
resolve the issue cleanly. For example, a helper like dma_get_hw_info()
returning struct dma_hw_info, whose first field is a hw_id, could work
well. Consumers could then use this helper, and if they know they are
dealing with a dw-edma channel, they can derive the LL location
straightforwardly as {hw_id * fixed_stride (e.g. PAGE_SIZE)}. Adding hw_id
to struct dma_slave_caps would make the necessary diff smaller, but I think
it would not semantically fit in the structure.

Thanks,
Koichiro

> 
> Frank
> 
> >
> > Regards,
> > Koichiro
> >
> > >
> > > Thanks for the review,
> > > Koichiro
> > >
> > > >
> > > > Frank
> > > > >
> > > > > Signed-off-by: Koichiro Den <den@valinux.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@synopsys.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
> > > > >

On Thu, Jan 22, 2026 at 10:19:24AM +0900, Koichiro Den wrote:
> On Wed, Jan 21, 2026 at 10:24:01AM -0500, Frank Li wrote:
> > On Wed, Jan 21, 2026 at 05:41:11PM +0900, Koichiro Den wrote:
> > > On Wed, Jan 21, 2026 at 10:38:53AM +0900, Koichiro Den wrote:
> > > > On Sun, Jan 18, 2026 at 12:05:47PM -0500, Frank Li wrote:
> > > > > 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.
> > > >
> > > > That makes sense, from an API cleanness perspective, thanks.
> > > > I'll add a helper function dw_pcie_edma_get_ll_region() in
> > > > drivers/pci/controller/dwc/pcie-designware.c, instead of the current
> > > > dw_edma_chan_get_ll_region() in dw-edma-core.c.
> > >
> > > Hi Frank,
> > >
> > > I looked into exposing LL regions from the EPC driver side, but the key
> > > issue is channel identification under possibly concurrent dmaengine users.
> > > In practice, the only stable handle a consumer has is a pointer to struct
> > > dma_chan, and the only reliable way to map that to the eDMA hardware
> > > channel is via dw_edma_chan->id.
> >
> > If possible, I suggest change to one page pre-channel. So there are a fixed
> > ll mapping.
>
> I agree that this would make the LL layout more deterministic and would
> indeed simplify locating the region for a given dw_edma_chan ID. That said,
> my concern was that even with a fixed per-channel layout, we still need a
> reliable way to map a struct dma_chan obtained by a consumer to the
> corresponding dw_edma_chan ID, especially in the presence of potentially
> concurrent dmaengine users.
>
> >
> > > I think an EPC-facing API would still need
> > > that mapping in any case, so keeping the helper in dw-edma seems simpler
> > > and more robust.
> > > If you have another idea, I'd appreciate your insights.
> >
> > I suggest add generally DMA engine API to get such property, some likes
> > a kind ioctrl \ dma_get_config().
>
> I think such a helper, combined with your one page per-channel idea, would
> resolve the issue cleanly. For example, a helper like dma_get_hw_info()
> returning struct dma_hw_info, whose first field is a hw_id, could work
> well. Consumers could then use this helper, and if they know they are
> dealing with a dw-edma channel, they can derive the LL location
> straightforwardly as {hw_id * fixed_stride (e.g. PAGE_SIZE)}. Adding hw_id
> to struct dma_slave_caps would make the necessary diff smaller, but I think
> it would not semantically fit in the structure.

It is worth to try.

Frank
>
> Thanks,
> Koichiro
>
> >
> > Frank
> >
> > >
> > > Regards,
> > > Koichiro
> > >
> > > >
> > > > Thanks for the review,
> > > > Koichiro
> > > >
> > > > >
> > > > > Frank
> > > > > >
> > > > > > Signed-off-by: Koichiro Den <den@valinux.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@synopsys.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
> > > > > >