linux-kernel - [RFC PATCH v3 17/35] dmaengine: dw-edma: Add helper func to retrieve register base and size

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Message-ID: <20251217151609.3162665-18-den@valinux.co.jp>
Date: Thu, 18 Dec 2025 00:15:51 +0900
From: Koichiro Den <den@...inux.co.jp>
To: Frank.Li@....com,
	dave.jiang@...el.com,
	ntb@...ts.linux.dev,
	linux-pci@...r.kernel.org,
	dmaengine@...r.kernel.org,
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Subject: [RFC PATCH v3 17/35] dmaengine: dw-edma: Add helper func to retrieve register base and size

Remote eDMA users (e.g. NTB) may need to expose the integrated DW eDMA
register block through a memory window.

Add a helper function that returns the physical base and size for a
given DesignWare EP controller.

Signed-off-by: Koichiro Den <den@...inux.co.jp>
---
 .../pci/controller/dwc/pcie-designware-ep.c   |  1 +
 drivers/pci/controller/dwc/pcie-designware.c  | 25 +++++++++++++++++++
 include/linux/dma/edma.h                      | 24 ++++++++++++++++++
 3 files changed, 50 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
index 9480aebaa32a..46d18e7945db 100644
--- a/drivers/pci/controller/dwc/pcie-designware-ep.c
+++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
@@ -12,6 +12,7 @@
 #include <linux/platform_device.h>
 
 #include "pcie-designware.h"
+#include <linux/dma/edma.h>
 #include <linux/pci-epc.h>
 #include <linux/pci-epf.h>
 
diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
index 75fc8b767fcc..1de88df7b1af 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;
 		}
 	}
 
@@ -1204,3 +1208,24 @@ 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, 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_base || !pci->edma.reg_phys)
+		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 3080747689f6..11d6eeb19fff 100644
--- a/include/linux/dma/edma.h
+++ b/include/linux/dma/edma.h
@@ -11,6 +11,7 @@
 
 #include <linux/device.h>
 #include <linux/dmaengine.h>
+#include <linux/pci-epc.h>
 
 #define EDMA_MAX_WR_CH                                  8
 #define EDMA_MAX_RD_CH                                  8
@@ -60,6 +61,27 @@ enum dw_edma_chip_flags {
 	DW_EDMA_CHIP_LOCAL	= BIT(0),
 };
 
+#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, size_t *sz);
+#else
+static inline int dw_edma_get_reg_window(struct pci_epc *epc, phys_addr_t *phys,
+					 size_t *sz)
+{
+	return -ENODEV;
+}
+#endif /* CONFIG_PCIE_DW */
+
 /**
  * struct dw_edma_chip - representation of DesignWare eDMA controller hardware
  * @dev:		 struct device of the eDMA controller
@@ -85,6 +107,8 @@ struct dw_edma_chip {
 	u32			flags;
 
 	void __iomem		*reg_base;
+	phys_addr_t		reg_phys;
+	size_t			reg_size;
 
 	u16			ll_wr_cnt;
 	u16			ll_rd_cnt;
-- 
2.51.0