Re: [PATCH v12 1/7] PCI: endpoint: Add auxiliary resource query API

On Fri, Apr 03, 2026 at 10:25:04PM +0530, Manivannan Sadhasivam wrote:
> On Tue, Mar 31, 2026 at 10:09:28AM -0400, Frank Li wrote:
> > On Tue, Mar 31, 2026 at 10:56:34PM +0900, Koichiro Den wrote:
> > > On Fri, Mar 27, 2026 at 12:31:09PM -0400, Frank Li wrote:
> > > > On Fri, Mar 27, 2026 at 12:54:16PM +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_count_aux_resources() / pci_epc_get_aux_resources() and the
> > > > > corresponding pci_epc_ops callbacks. The count helper returns the number
> > > > > of available resources via an output parameter, while the get helper
> > > > > fills a caller-provided array of resources described by type, physical
> > > > > address and size, plus type-specific metadata.
> > > > >
> > > > > Suggested-by: Manivannan Sadhasivam <[email protected]>
> > > > > Signed-off-by: Koichiro Den <[email protected]>
> > > > > ---
> > > > > Changes in v12:
> > > > >   - Add pci_epc_count_aux_resources() and pci_epc_ops.count_aux_resources
> > > > >   - Use pci_epc_function_is_valid() instead of open-coding
> > > > >
> > > > >  drivers/pci/endpoint/pci-epc-core.c | 83 +++++++++++++++++++++++++++++
> > > > >  include/linux/pci-epc.h             | 53 ++++++++++++++++++
> > > > >  2 files changed, 136 insertions(+)
> > > > >
> > > > > diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
> > > > > index 6c3c58185fc5..fded71a19d71 100644
> > > > > --- a/drivers/pci/endpoint/pci-epc-core.c
> > > > > +++ b/drivers/pci/endpoint/pci-epc-core.c
> > > > > @@ -156,6 +156,89 @@ const struct pci_epc_features *pci_epc_get_features(struct pci_epc *epc,
> > > > >  }
> > > > >  EXPORT_SYMBOL_GPL(pci_epc_get_features);
> > > > >
> > > > > +/**
> > > > > + * pci_epc_count_aux_resources() - count EPC-provided auxiliary resources
> > > > > + * @epc: EPC device
> > > > > + * @func_no: function number
> > > > > + * @vfunc_no: virtual function number
> > > > > + * @num_resources: returned number of auxiliary resources
> > > > > + *
> > > > > + * 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 how many such resources the backend
> > > > > + * provides.
> > > > > + *
> > > > > + * Return: 0 on success, -EOPNOTSUPP if the backend does not support auxiliary
> > > > > + * resource queries, or another -errno on failure.
> > > > > + */
> > > > > +int pci_epc_count_aux_resources(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> > > > > +				int *num_resources)
> > > >
> > > > Most like such kinds APIs return count directly,
> > > >   < 0,  means error.
> > > >  >= 0,  means how many resource.
> > >
> > > I chose to return 0 on success here based on Mani's earlier feedback on v11:
> > > https://lore.kernel.org/linux-pci/lfbv6sjevz4xtjr6zt2hl3wap3bfwkvigqb6fdztqmutxgcvld@3t4x5gstr4nj/
> > 
> > I am okay for both, But may request Mani think 2nd. Most existing kernel
> > API use return value for count of resource.
> > 
> 
> Ok, fine with me.
> 
> @Koichiro Den: When you respin, could you please rename the API to
> pci_epc_get_aux_resources_count()?

Alright, thank you both!

Koichiro

> 
> Reset LGTM!
> 
> - Mani
> 
> -- 
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