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:

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On Wed, Jan 21, 2026 at 05:41:11PM +0900, Koichiro Den wrote:

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On Wed, Jan 21, 2026 at 10:38:53AM +0900, Koichiro Den wrote:

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

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On Sun, Jan 18, 2026 at 10:54:07PM +0900, Koichiro Den wrote:

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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.

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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

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Frank

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Regards,
Koichiro

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Thanks for the review,
Koichiro

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Frank

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Signed-off-by: Koichiro Den <redacted>
---
 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