linux-kernel - [PATCH 2/2] PCI: dwc: Add helper to query integrated dw-edma linked-list region

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Message-ID: <20260126071550.3233631-3-den@valinux.co.jp>
Date: Mon, 26 Jan 2026 16:15:50 +0900
From: Koichiro Den <den@...inux.co.jp>
To: jingoohan1@...il.com,
	mani@...nel.org,
	lpieralisi@...nel.org,
	kwilczynski@...nel.org,
	robh@...nel.org,
	bhelgaas@...gle.com,
	Frank.Li@....com
Cc: linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] PCI: dwc: Add helper to query integrated dw-edma linked-list region

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)
+{
+	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