Re: [PATCH v2 7/7] PCI: dwc: Add helper to query integrated dw-edma linked-list region

[Frank Li <Frank.li@nxp.com>]

On Thu, Jan 29, 2026 at 01:25:30AM +0900, Koichiro Den wrote:
> On Wed, Jan 28, 2026 at 10:48:04AM -0500, Frank Li wrote:
> > On Tue, Jan 27, 2026 at 12:34:20PM +0900, Koichiro Den wrote:
> > > Some DesignWare PCIe endpoint controllers integrate a DesignWare eDMA
> > > instance and allocate per-channel linked-list (LL) regions. Remote eDMA
> > > providers may need to expose those LL regions to the host so it can
> > > build descriptors against the remote view.
> > >
> > > Export dwc_pcie_edma_get_ll_region() to allow higher-level code to query
> > > the LL region (base/size) for a given EPC, transfer direction
> > > (DMA_DEV_TO_MEM / DMA_MEM_TO_DEV) and hardware channel identifier. The
> > > helper maps the request to the appropriate read/write LL region
> > > depending on whether the integrated eDMA is the local or the remote
> > > view.
> > >
> > > Signed-off-by: Koichiro Den <den@valinux.co.jp>
> > > ---
> > >  drivers/pci/controller/dwc/pcie-designware.c | 45 ++++++++++++++++++++
> > >  include/linux/pcie-dwc-edma.h                | 33 ++++++++++++++
> > >  2 files changed, 78 insertions(+)
> > >
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > > index bbaeecce199a..e8617873e832 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > @@ -1369,3 +1369,48 @@ int dwc_pcie_edma_get_reg_window(struct pci_epc *epc, phys_addr_t *phys,
> > >  	return 0;
> > >  }
> > >  EXPORT_SYMBOL_GPL(dwc_pcie_edma_get_reg_window);
> > > +
> > > +int dwc_pcie_edma_get_ll_region(struct pci_epc *epc,
> > > +				enum dma_transfer_direction dir, int hw_id,
> > > +				struct dw_edma_region *region)
> >
> > These APIs need an user, A simple method is that add one test case in
> > pci-epf-test.
>
> Thanks for the feedback.
>
> I'm unsure whether adding DesignWare-specific coverage to pci-epf-test
> would be acceptable. I'd appreciate your guidance on the preferred
> approach.
>
> One possible direction I had in mind is to keep pci-epf-test.c generic and

Add a EPC/EPF API, so dynatmic check if support DMA region or other feature.

Frank

> add an optional DesignWare-specific extension, selected via Kconfig, to
> exercise these helpers. Likewise on the host side
> (drivers/misc/pci_endpoint_test.c and kselftest pci_endpoint_test.c).
>
> Koichiro
>
> >
> > Frank
> >
> > > +{
> > > +	struct dw_edma_chip *chip;
> > > +	struct dw_pcie_ep *ep;
> > > +	struct dw_pcie *pci;
> > > +	bool dir_read;
> > > +
> > > +	if (!epc || !region)
> > > +		return -EINVAL;
> > > +	if (dir != DMA_DEV_TO_MEM && dir != DMA_MEM_TO_DEV)
> > > +		return -EINVAL;
> > > +	if (hw_id < 0)
> > > +		return -EINVAL;
> > > +
> > > +	ep = epc_get_drvdata(epc);
> > > +	if (!ep)
> > > +		return -ENODEV;
> > > +
> > > +	pci = to_dw_pcie_from_ep(ep);
> > > +	chip = &pci->edma;
> > > +
> > > +	if (!chip->dev)
> > > +		return -ENODEV;
> > > +
> > > +	if (chip->flags & DW_EDMA_CHIP_LOCAL)
> > > +		dir_read = (dir == DMA_DEV_TO_MEM);
> > > +	else
> > > +		dir_read = (dir == DMA_MEM_TO_DEV);
> > > +
> > > +	if (dir_read) {
> > > +		if (hw_id >= chip->ll_rd_cnt)
> > > +			return -EINVAL;
> > > +		*region = chip->ll_region_rd[hw_id];
> > > +	} else {
> > > +		if (hw_id >= chip->ll_wr_cnt)
> > > +			return -EINVAL;
> > > +		*region = chip->ll_region_wr[hw_id];
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +EXPORT_SYMBOL_GPL(dwc_pcie_edma_get_ll_region);
> > > diff --git a/include/linux/pcie-dwc-edma.h b/include/linux/pcie-dwc-edma.h
> > > index a5b0595603f4..36afb4df1998 100644
> > > --- a/include/linux/pcie-dwc-edma.h
> > > +++ b/include/linux/pcie-dwc-edma.h
> > > @@ -6,6 +6,8 @@
> > >  #ifndef LINUX_PCIE_DWC_EDMA_H
> > >  #define LINUX_PCIE_DWC_EDMA_H
> > >
> > > +#include <linux/dma/edma.h>
> > > +#include <linux/dmaengine.h>
> > >  #include <linux/errno.h>
> > >  #include <linux/kconfig.h>
> > >  #include <linux/pci-epc.h>
> > > @@ -27,6 +29,29 @@
> > >   */
> > >  int dwc_pcie_edma_get_reg_window(struct pci_epc *epc, phys_addr_t *phys,
> > >  				 resource_size_t *sz);
> > > +
> > > +/**
> > > + * dwc_pcie_edma_get_ll_region() - get linked-list (LL) region for a HW channel
> > > + * @epc:    EPC device associated with the integrated eDMA instance
> > > + * @dir:    DMA transfer direction (%DMA_DEV_TO_MEM or %DMA_MEM_TO_DEV)
> > > + * @hw_id:  hardware channel identifier (equals to dw_edma_chan.id)
> > > + * @region: pointer to a region descriptor to fill in
> > > + *
> > > + * Some integrated DesignWare eDMA instances allocate per-channel linked-list
> > > + * (LL) regions for descriptor storage. This helper returns the LL region
> > > + * corresponding to @dir and @hw_id.
> > > + *
> > > + * The mapping between @dir and the underlying eDMA read/write LL region
> > > + * depends on whether the integrated eDMA instance represents a local or a
> > > + * remote view.
> > > + *
> > > + * Return: 0 on success, -EINVAL on invalid arguments (including out-of-range
> > > + *         @hw_id), or -ENODEV if the integrated eDMA instance is not present
> > > + *         or not initialized.
> > > + */
> > > +int dwc_pcie_edma_get_ll_region(struct pci_epc *epc,
> > > +				enum dma_transfer_direction dir, int hw_id,
> > > +				struct dw_edma_region *region);
> > >  #else
> > >  static inline int
> > >  dwc_pcie_edma_get_reg_window(struct pci_epc *epc, phys_addr_t *phys,
> > > @@ -34,6 +59,14 @@ dwc_pcie_edma_get_reg_window(struct pci_epc *epc, phys_addr_t *phys,
> > >  {
> > >  	return -ENODEV;
> > >  }
> > > +
> > > +static inline int
> > > +dwc_pcie_edma_get_ll_region(struct pci_epc *epc,
> > > +			    enum dma_transfer_direction dir, int hw_id,
> > > +			    struct dw_edma_region *region)
> > > +{
> > > +	return -ENODEV;
> > > +}
> > >  #endif /* CONFIG_PCIE_DW */
> > >
> > >  #endif /* LINUX_PCIE_DWC_EDMA_H */
> > > --
> > > 2.51.0
> > >