[RFC PATCH v4 01/38] dmaengine: dw-edma: Export helper to get integrated register window

Koichiro Den
2026-01-18T13:55:00Z

Some DesignWare PCIe endpoint controllers integrate a DesignWare eDMA
instance. Remote-eDMA providers (e.g. vNTB) need to expose the eDMA
register block to the host through a memory window so the host can
ioremap it and run dw_edma_probe() against the remote view.

Record the physical base and size of the eDMA register aperture and
export dw_edma_get_reg_window() so higher-level code can query the
register window associated with a given PCI EPC device.

Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
drivers/pci/controller/dwc/pcie-designware.c | 26 ++++++++++++++++++++
include/linux/dma/edma.h | 25 +++++++++++++++++++
2 files changed, 51 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
index 345365ea97c7..ad18b84c9f71 100644
--- a/drivers/pci/controller/dwc/pcie-designware.c
+++ b/drivers/pci/controller/dwc/pcie-designware.c
@@ -162,8 +162,12 @@ int dw_pcie_get_resources(struct dw_pcie *pci)
pci->edma.reg_base = devm_ioremap_resource(pci->dev, res);
if (IS_ERR(pci->edma.reg_base))
return PTR_ERR(pci->edma.reg_base);
+ pci->edma.reg_phys = res->start;
+ pci->edma.reg_size = resource_size(res);
} else if (pci->atu_size >= 2 * DEFAULT_DBI_DMA_OFFSET) {
pci->edma.reg_base = pci->atu_base + DEFAULT_DBI_DMA_OFFSET;
+ pci->edma.reg_phys = pci->atu_phys_addr + DEFAULT_DBI_DMA_OFFSET;
+ pci->edma.reg_size = pci->atu_size - DEFAULT_DBI_DMA_OFFSET;
}
}

@@ -1257,3 +1261,25 @@ resource_size_t dw_pcie_parent_bus_offset(struct dw_pcie *pci,

return cpu_phys_addr - reg_addr;
}
+
+int dw_edma_get_reg_window(struct pci_epc *epc, phys_addr_t *phys,
+ resource_size_t *sz)
+{
+ struct dw_pcie_ep *ep = epc_get_drvdata(epc);
+ struct dw_pcie *pci;
+
+ if (!ep)
+ return -ENODEV;
+
+ pci = to_dw_pcie_from_ep(ep);
+ if (!pci->edma.reg_size)
+ return -ENODEV;
+
+ if (phys)
+ *phys = pci->edma.reg_phys;
+ if (sz)
+ *sz = pci->edma.reg_size;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(dw_edma_get_reg_window);
diff --git a/include/linux/dma/edma.h b/include/linux/dma/edma.h
index 270b5458aecf..ffad10ff2cd6 100644
--- a/include/linux/dma/edma.h
+++ b/include/linux/dma/edma.h
@@ -83,6 +83,8 @@ struct dw_edma_chip {
u32 flags;

void __iomem *reg_base;
+ phys_addr_t reg_phys;
+ resource_size_t reg_size;

u16 ll_wr_cnt;
u16 ll_rd_cnt;
@@ -115,4 +117,27 @@ static inline int dw_edma_remove(struct dw_edma_chip *chip)
}
#endif /* CONFIG_DW_EDMA */

+struct pci_epc;
+
+#if IS_REACHABLE(CONFIG_PCIE_DW)
+/**
+ * dw_edma_get_reg_window - get eDMA register base and size
+ * @epc: the EPC device with which the eDMA instance is integrated
+ * @phys: the output parameter that returns the register base address
+ * @sz: the output parameter that returns the register space size
+ *
+ * Remote eDMA users (e.g. NTB) may need to expose the integrated DW eDMA
+ * register block through a memory window. This helper returns the physical
+ * base and size for a given DesignWare EP controller.
+ */
+int dw_edma_get_reg_window(struct pci_epc *epc, phys_addr_t *phys,
+ resource_size_t *sz);
+#else
+static inline int dw_edma_get_reg_window(struct pci_epc *epc, phys_addr_t *phys,
+ resource_size_t *sz)
+{
+ return -ENODEV;
+}
+#endif /* CONFIG_PCIE_DW */
+
#endif /* _DW_EDMA_H */
--
2.51.0