Re: [PATCH v8 3/9] PCI: endpoint: Add auxiliary resource query API

On Tue, Feb 17, 2026 at 05:05:55PM +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_aux_resources() and the corresponding pci_epc_ops
> get_aux_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 <[email protected]>
> ---
Reviewed-by: Frank Li <[email protected]>
> Changes since v7:
>   - Add a 'data' field in pci_epc_aux_resource.u.db_mmio.
>   - Add comments describing the type-specific metadata fields.
>
>  drivers/pci/endpoint/pci-epc-core.c | 41 +++++++++++++++++++++++
>  include/linux/pci-epc.h             | 52 +++++++++++++++++++++++++++++
>  2 files changed, 93 insertions(+)
>
> diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
> index 068155819c57..01de4bd5047a 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_aux_resources() - query EPC-provided auxiliary resources
> + * @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 auxiliary resource queries
> + *   * other -errno on failure
> + */
> +int pci_epc_get_aux_resources(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> +			      struct pci_epc_aux_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_aux_resources)
> +		return -EOPNOTSUPP;
> +
> +	mutex_lock(&epc->lock);
> +	ret = epc->ops->get_aux_resources(epc, func_no, vfunc_no, resources,
> +					  num_resources);
> +	mutex_unlock(&epc->lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(pci_epc_get_aux_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 7a87f5962dd0..c68aaaf3542a 100644
> --- a/include/linux/pci-epc.h
> +++ b/include/linux/pci-epc.h
> @@ -61,6 +61,51 @@ struct pci_epc_map {
>  	void __iomem	*virt_addr;
>  };
>
> +/**
> + * enum pci_epc_aux_resource_type - auxiliary resource type identifiers
> + * @PCI_EPC_AUX_DMA_CTRL_MMIO: Integrated DMA controller register window (MMIO)
> + * @PCI_EPC_AUX_DMA_CHAN_DESC: Per-channel DMA descriptor
> + * @PCI_EPC_AUX_DOORBELL_MMIO: Doorbell MMIO, that might be outside the DMA
> + *                             controller register window
> + *
> + * 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_aux_resource_type {
> +	PCI_EPC_AUX_DMA_CTRL_MMIO,
> +	PCI_EPC_AUX_DMA_CHAN_DESC,
> +	PCI_EPC_AUX_DOORBELL_MMIO,
> +};
> +
> +/**
> + * struct pci_epc_aux_resource - a physical auxiliary resource that may be
> + *                               exposed for peer use
> + * @type:       resource type, see enum pci_epc_aux_resource_type
> + * @phys_addr:  physical base address of the resource
> + * @size:       size of the resource in bytes
> + * @bar:        BAR number where this resource is already exposed to the RC
> + *              (NO_BAR if not)
> + * @bar_offset: offset within @bar where the resource starts (valid iff
> + *              @bar != NO_BAR)
> + * @u:          type-specific metadata
> + */
> +struct pci_epc_aux_resource {
> +	enum pci_epc_aux_resource_type type;
> +	phys_addr_t phys_addr;
> +	resource_size_t size;
> +	enum pci_barno bar;
> +	resource_size_t bar_offset;
> +
> +	union {
> +		/* PCI_EPC_AUX_DOORBELL_MMIO */
> +		struct {
> +			int irq; /* IRQ number for the doorbell handler */
> +			u32 data; /* write value to ring the doorbell */
> +		} db_mmio;
> +	} u;
> +};
> +
>  /**
>   * struct pci_epc_ops - set of function pointers for performing EPC operations
>   * @write_header: ops to populate configuration space header
> @@ -84,6 +129,7 @@ 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_aux_resources: ops to retrieve controller-owned auxiliary resources
>   * @owner: the module owner containing the ops
>   */
>  struct pci_epc_ops {
> @@ -115,6 +161,9 @@ 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_aux_resources)(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> +				     struct pci_epc_aux_resource *resources,
> +				     int num_resources);
>  	struct module *owner;
>  };
>
> @@ -337,6 +386,9 @@ 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_aux_resources(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> +			      struct pci_epc_aux_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
>