Re: [PATCH v8 2/5] PCI: endpoint: Add BAR subrange mapping support

Koichiro Den
2026-01-19T08:43:04Z

On Thu, Jan 15, 2026 at 09:52:58AM -0500, Frank Li wrote:
> On Thu, Jan 15, 2026 at 05:49:25PM +0900, Koichiro Den wrote:
> > Extend the PCI endpoint core to support mapping subranges within a BAR.
> > Add an optional 'submap' field in struct pci_epf_bar so an endpoint
> > function driver can request inbound mappings that fully cover the BAR.
> >
> > Introduce a new EPC feature bit, subrange_mapping, and reject submap
> > requests from pci_epc_set_bar() unless the controller advertises both
> > subrange_mapping and dynamic_inbound_mapping features.
> >
> > The submap array describes the complete BAR layout (no overlaps and no
> > gaps are allowed to avoid exposing untranslated address ranges). This
> > provides the generic infrastructure needed to map multiple logical
> > regions into a single BAR at different offsets, without assuming a
> > controller-specific inbound address translation mechanism.
> >
> > Signed-off-by: Koichiro Den <den@valinux.co.jp>
> > ---
> > drivers/pci/endpoint/pci-epc-core.c | 8 ++++++++
> > include/linux/pci-epc.h | 4 ++++
> > include/linux/pci-epf.h | 27 +++++++++++++++++++++++++++
> > 3 files changed, 39 insertions(+)
> >
> > diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
> > index ca7f19cc973a..068155819c57 100644
> > --- a/drivers/pci/endpoint/pci-epc-core.c
> > +++ b/drivers/pci/endpoint/pci-epc-core.c
> > @@ -596,6 +596,14 @@ int pci_epc_set_bar(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> > if (!epc_features)
> > return -EINVAL;
> >
> > + if (epf_bar->num_submap && !epf_bar->submap)
> > + return -EINVAL;
> > +
> > + if (epf_bar->num_submap &&
> > + !(epc_features->dynamic_inbound_mapping &&
> > + epc_features->subrange_mapping))
> > + return -EINVAL;
> > +
> > if (epc_features->bar[bar].type == BAR_RESIZABLE &&
> > (epf_bar->size < SZ_1M || (u64)epf_bar->size > (SZ_128G * 1024)))
> > return -EINVAL;
> > diff --git a/include/linux/pci-epc.h b/include/linux/pci-epc.h
> > index 4c8516756c56..c021c7af175f 100644
> > --- a/include/linux/pci-epc.h
> > +++ b/include/linux/pci-epc.h
> > @@ -227,6 +227,9 @@ struct pci_epc_bar_desc {
> > * inbound mappings for an already configured BAR
> > * (i.e. allow calling pci_epc_set_bar() again
> > * without first calling pci_epc_clear_bar())
> > + * @subrange_mapping: indicate if the EPC device can map inbound subranges for a
> > + * BAR. This feature depends on @dynamic_inbound_mapping
> > + * feature.
> > * @msi_capable: indicate if the endpoint function has MSI capability
> > * @msix_capable: indicate if the endpoint function has MSI-X capability
> > * @intx_capable: indicate if the endpoint can raise INTx interrupts
> > @@ -236,6 +239,7 @@ struct pci_epc_bar_desc {
> > struct pci_epc_features {
> > unsigned int linkup_notifier : 1;
> > unsigned int dynamic_inbound_mapping : 1;
> > + unsigned int subrange_mapping : 1;
> > unsigned int msi_capable : 1;
> > unsigned int msix_capable : 1;
> > unsigned int intx_capable : 1;
> > diff --git a/include/linux/pci-epf.h b/include/linux/pci-epf.h
> > index 48f68c4dcfa5..46f817da6e24 100644
> > --- a/include/linux/pci-epf.h
> > +++ b/include/linux/pci-epf.h
> > @@ -110,6 +110,26 @@ struct pci_epf_driver {
> >
> > #define to_pci_epf_driver(drv) container_of_const((drv), struct pci_epf_driver, driver)
> >
> > +/**
> > + * struct pci_epf_bar_submap - BAR subrange for inbound mapping
> > + * @phys_addr: target physical/DMA address for this subrange
> > + * @size: the size of the subrange to be mapped
> > + *
> > + * When pci_epf_bar.num_submap is >0, pci_epf_bar.submap describes the
> > + * complete BAR layout. This allows an EPC driver to program multiple
> > + * inbound translation windows for a single BAR when supported by the
> > + * controller. The array order defines the BAR layout (submap[0] at offset
> > + * 0, and each immediately follows the previous one).
> > + *
> > + * Note that the subranges:
> > + * - must be non-overlapping
> > + * - must exactly cover the BAR (i.e. no holes)
>
> It is impossible after use 'size'. It can be removed.

Agreed, those notes (ie non-overlapping/no holes) are redundant now.
Thanks for pointing it out. I'll drop them.

Koichiro

>
> > + */
> > +struct pci_epf_bar_submap {
> > + dma_addr_t phys_addr;
> > + size_t size;
> > +};
> > +
> > /**
> > * struct pci_epf_bar - represents the BAR of EPF device
> > * @phys_addr: physical address that should be mapped to the BAR
> > @@ -119,6 +139,9 @@ struct pci_epf_driver {
> > * requirement
> > * @barno: BAR number
> > * @flags: flags that are set for the BAR
> > + * @num_submap: number of entries in @submap
> > + * @submap: array of subrange descriptors allocated by the caller. See
> > + * struct pci_epf_bar_submap for the restrictions in detail.
> > */
> > struct pci_epf_bar {
> > dma_addr_t phys_addr;
> > @@ -127,6 +150,10 @@ struct pci_epf_bar {
> > size_t mem_size;
> > enum pci_barno barno;
> > int flags;
> > +
> > + /* Optional sub-range mapping */
> > + unsigned int num_submap;
> > + struct pci_epf_bar_submap *submap;
>
> struct pci_epf_bar_submap submap[] __counted_by(num_submap);
>
> Not sure if use this simplify alloc/free.
>
> Frank
> > };
> >
> > /**
> > --
> > 2.51.0
> >