Re: [PATCH v3 06/11] PCI: endpoint: Add remote resource query API

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

On Thu, Feb 05, 2026 at 03:53:52PM +0900, Koichiro Den wrote:
> On Wed, Feb 04, 2026 at 12:55:58PM -0500, Frank Li wrote:
> > On Wed, Feb 04, 2026 at 11:54:34PM +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
> > > + * @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..af60d4ad2f0e 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;
> >
> > is it good use struct resource?
>
> Personally I don't think it's the best fit here, since these remote
> resources are not meant to participate in the global resource tree or
> managed by the resource management framework. And most of struct resource
> fields (name/flags and the links) does not make sense in this context.
>
> >
> > > +
> > > +	union {
> > > +		/* PCI_EPC_RR_DMA_CHAN_DESC */
> > > +		struct {
> > > +			u16 hw_chan_id;
> > > +			bool ep2rc;
> > > +		} 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)
> >
> > Add comments, must set 'type' of pci_epc_remote_resource.
>
> Would something like the following address your concern?
>
>     * @get_remote_resources: ops to retrieve controller-owned resources that can be
>     *                        exposed to the remote host (optional)
>   + *                        The callback fills @resources (up to @num_resources entries)
>   + *                        and returns the number of valid entries. Each returned entry
>   + *                        must have @type set (which selects the valid union member in @u)
>   + *                        and provide valid @phys_addr/@sizei.

After I review your next patch, I understand API here. It is good.

Frank

>
> Thanks for the review,
> Koichiro
>
> >
> > Over all it is good.
> >
> > Frank
> > >   * @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
> > >