linux-kernel - Re: [PATCH v2 7/7] PCI: dwc: Add helper to query integrated dw-edma linked-list region

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Message-ID: <aXovtOcilRrkA0Ot@lizhi-Precision-Tower-5810>
Date: Wed, 28 Jan 2026 10:48:04 -0500
From: Frank Li <Frank.li@....com>
To: Koichiro Den <den@...inux.co.jp>
Cc: vkoul@...nel.org, mani@...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 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.

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
>