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

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Message-ID: <20260118135440.1958279-2-den@valinux.co.jp>
Date: Sun, 18 Jan 2026 22:54:03 +0900
From: Koichiro Den <den@...inux.co.jp>
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Subject: [RFC PATCH v4 01/38] dmaengine: dw-edma: Export helper to get integrated register window

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@...inux.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