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Message-ID: <aYOILtPYxazppfRD@lizhi-Precision-Tower-5810>
Date: Wed, 4 Feb 2026 12:55:58 -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 v3 06/11] PCI: endpoint: Add remote resource query API
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@...inux.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?
> +
> + 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.
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
>
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