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Message-ID: <dpx4s35dqvhp54sloixxsn3qcf3g2k745wieaefdc2svgkbtr6@4vuqgp46czi7>
Date: Thu, 29 Jan 2026 01:25:30 +0900
From: Koichiro Den <den@...inux.co.jp>
To: Frank Li <Frank.li@....com>, mani@...nel.org
Cc: vkoul@...nel.org, jingoohan1@...il.com, lpieralisi@...nel.org,
kwilczynski@...nel.org, robh@...nel.org, bhelgaas@...gle.com, dmaengine@...r.kernel.org,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 7/7] PCI: dwc: Add helper to query integrated dw-edma
linked-list region
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@...inux.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 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
> >
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