Re: [PATCH v4 4/9] PCI: endpoint: Add remote resource query API

[Frank Li <Frank.li@nxp.com>]

On Sat, Feb 07, 2026 at 02:26:41AM +0900, Koichiro Den wrote:
> Endpoint controller drivers may integrate auxiliary blocks (e.g. DMA
> engines) whose register windows and descriptor memories metadata need to
> be exposed to a remote peer. Endpoint function drivers need a generic
> way to discover such resources without hard-coding controller-specific
> helpers.
>
> Add pci_epc_get_remote_resources() and the corresponding pci_epc_ops
> get_remote_resources() callback. The API returns a list of resources
> described by type, physical address and size, plus type-specific
> metadata.
>
> Passing resources == NULL (or num_resources == 0) returns the required
> number of entries.
>
> Signed-off-by: Koichiro Den <den@valinux.co.jp>
> ---
>  drivers/pci/endpoint/pci-epc-core.c | 41 +++++++++++++++++++++++++
>  include/linux/pci-epc.h             | 46 +++++++++++++++++++++++++++++
>  2 files changed, 87 insertions(+)
>
> diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
> index 068155819c57..fa161113e24c 100644
> --- a/drivers/pci/endpoint/pci-epc-core.c
> +++ b/drivers/pci/endpoint/pci-epc-core.c
> @@ -155,6 +155,47 @@ const struct pci_epc_features *pci_epc_get_features(struct pci_epc *epc,
>  }
>  EXPORT_SYMBOL_GPL(pci_epc_get_features);
>
> +/**
> + * pci_epc_get_remote_resources() - query EPC-provided remote resources

I am not sure if it good naming, pci_epc_get_additional_resources().
Niklas Cassel may have good suggest, I just find you forget cc him.

Frank
> + * @epc: EPC device
> + * @func_no: function number
> + * @vfunc_no: virtual function number
> + * @resources: output array (may be NULL to query required count)
> + * @num_resources: size of @resources array in entries (0 when querying count)
> + *
> + * Some EPC backends integrate auxiliary blocks (e.g. DMA engines) whose control
> + * registers and/or descriptor memories can be exposed to the host by mapping
> + * them into BAR space. This helper queries the backend for such resources.
> + *
> + * Return:
> + *   * >= 0: number of resources returned (or required, if @resources is NULL)
> + *   * -EOPNOTSUPP: backend does not support remote resource queries
> + *   * other -errno on failure
> + */
> +int pci_epc_get_remote_resources(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> +				 struct pci_epc_remote_resource *resources,
> +				 int num_resources)
> +{
> +	int ret;
> +
> +	if (!epc || !epc->ops)
> +		return -EINVAL;
> +
> +	if (func_no >= epc->max_functions)
> +		return -EINVAL;
> +
> +	if (!epc->ops->get_remote_resources)
> +		return -EOPNOTSUPP;
> +
> +	mutex_lock(&epc->lock);
> +	ret = epc->ops->get_remote_resources(epc, func_no, vfunc_no,
> +					     resources, num_resources);
> +	mutex_unlock(&epc->lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(pci_epc_get_remote_resources);
> +
>  /**
>   * pci_epc_stop() - stop the PCI link
>   * @epc: the link of the EPC device that has to be stopped
> diff --git a/include/linux/pci-epc.h b/include/linux/pci-epc.h
> index c021c7af175f..7d2fce9f3a63 100644
> --- a/include/linux/pci-epc.h
> +++ b/include/linux/pci-epc.h
> @@ -61,6 +61,44 @@ struct pci_epc_map {
>  	void __iomem	*virt_addr;
>  };
>
> +/**
> + * enum pci_epc_remote_resource_type - remote resource type identifiers
> + * @PCI_EPC_RR_DMA_CTRL_MMIO: Integrated DMA controller register window (MMIO)
> + * @PCI_EPC_RR_DMA_CHAN_DESC: Per-channel DMA descriptor
> + *
> + * EPC backends may expose auxiliary blocks (e.g. DMA engines) by mapping their
> + * register windows and descriptor memories into BAR space. This enum
> + * identifies the type of each exposable resource.
> + */
> +enum pci_epc_remote_resource_type {
> +	PCI_EPC_RR_DMA_CTRL_MMIO,
> +	PCI_EPC_RR_DMA_CHAN_DESC,
> +};
> +
> +/**
> + * struct pci_epc_remote_resource - a physical resource that can be exposed
> + * @type:      resource type, see enum pci_epc_remote_resource_type
> + * @phys_addr: physical base address of the resource
> + * @size:      size of the resource in bytes
> + * @u:         type-specific metadata
> + *
> + * For @PCI_EPC_RR_DMA_CHAN_DESC, @u.dma_chan_desc provides per-channel
> + * information.
> + */
> +struct pci_epc_remote_resource {
> +	enum pci_epc_remote_resource_type type;
> +	phys_addr_t phys_addr;
> +	resource_size_t size;
> +
> +	union {
> +		/* PCI_EPC_RR_DMA_CHAN_DESC */
> +		struct {
> +			int irq;
> +			resource_size_t db_offset;
> +		} dma_chan_desc;
> +	} u;
> +};
> +
>  /**
>   * struct pci_epc_ops - set of function pointers for performing EPC operations
>   * @write_header: ops to populate configuration space header
> @@ -84,6 +122,8 @@ struct pci_epc_map {
>   * @start: ops to start the PCI link
>   * @stop: ops to stop the PCI link
>   * @get_features: ops to get the features supported by the EPC
> + * @get_remote_resources: ops to retrieve controller-owned resources that can be
> + *			  exposed to the remote host (optional)
>   * @owner: the module owner containing the ops
>   */
>  struct pci_epc_ops {
> @@ -115,6 +155,9 @@ struct pci_epc_ops {
>  	void	(*stop)(struct pci_epc *epc);
>  	const struct pci_epc_features* (*get_features)(struct pci_epc *epc,
>  						       u8 func_no, u8 vfunc_no);
> +	int	(*get_remote_resources)(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> +					struct pci_epc_remote_resource *resources,
> +					int num_resources);
>  	struct module *owner;
>  };
>
> @@ -309,6 +352,9 @@ int pci_epc_start(struct pci_epc *epc);
>  void pci_epc_stop(struct pci_epc *epc);
>  const struct pci_epc_features *pci_epc_get_features(struct pci_epc *epc,
>  						    u8 func_no, u8 vfunc_no);
> +int pci_epc_get_remote_resources(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> +				 struct pci_epc_remote_resource *resources,
> +				 int num_resources);
>  enum pci_barno
>  pci_epc_get_first_free_bar(const struct pci_epc_features *epc_features);
>  enum pci_barno pci_epc_get_next_free_bar(const struct pci_epc_features
> --
> 2.51.0
>