Re: [PATCH v10 1/7] PCI: endpoint: Add auxiliary resource query API

On Mon, Mar 02, 2026 at 04:14:21PM +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.
> 
> Reviewed-by: Frank Li <[email protected]>
> Tested-by: Niklas Cassel <[email protected]>
> Signed-off-by: Koichiro Den <[email protected]>
> ---
>  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 32cf9a9bc365..d63967622505 100644
> --- a/drivers/pci/endpoint/pci-epc-core.c
> +++ b/drivers/pci/endpoint/pci-epc-core.c
> @@ -157,6 +157,47 @@ 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 63a24ebf144c..0827650acf93 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,

I see that these resources are only used in [1], which is still in early stage.
It'd help if you can just keep DOORBELL_MMIO resource related code in this
series and add these resources when required.

- Mani

[1] https://lore.kernel.org/linux-pci/[email protected]

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