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 <[email protected]> > > > > --- > > > > 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 <[email protected]>"); > > > > 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 > > > >
