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Message-ID: <ihe4sguchgrbiskeq5ht3tcti7yjzhsdhu7nobvbejbqtlr7dd@3n6p2poipy6d>
Date: Sun, 8 Feb 2026 01:39:40 +0900
From: Koichiro Den <den@...inux.co.jp>
To: Frank Li <Frank.li@....com>, cassel@...nel.org
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-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/9] PCI: endpoint: Add remote resource query API
On Fri, Feb 06, 2026 at 01:01:33PM -0500, Frank Li wrote:
> 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@...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
>
> 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.
That's true, I just naively followed the get_maintainers.pl output.
Niklas, I'd be happy to hear your thoughts on the naming here.
One other option I had in mind after Frank's feedback is
pci_epc_get_aux_resources().
Thanks,
Koichiro
>
> 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
> >
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