Re: [PATCH v10 1/7] PCI: endpoint: Add auxiliary resource query API

On Sat, Mar 21, 2026 at 07:47:32PM +0530, Manivannan Sadhasivam wrote:
> On Mon, Mar 02, 2026 at 04:14:21PM +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_aux_resources() and the corresponding pci_epc_ops
> > get_aux_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.
> > 
> > Reviewed-by: Frank Li <[email protected]>
> > Tested-by: Niklas Cassel <[email protected]>
> > Signed-off-by: Koichiro Den <[email protected]>
> > ---
> >  drivers/pci/endpoint/pci-epc-core.c | 41 +++++++++++++++++++++++
> >  include/linux/pci-epc.h             | 52 +++++++++++++++++++++++++++++
> >  2 files changed, 93 insertions(+)
> > 
> > diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
> > index 32cf9a9bc365..d63967622505 100644
> > --- a/drivers/pci/endpoint/pci-epc-core.c
> > +++ b/drivers/pci/endpoint/pci-epc-core.c
> > @@ -157,6 +157,47 @@ const struct pci_epc_features *pci_epc_get_features(struct pci_epc *epc,
> >  }
> >  EXPORT_SYMBOL_GPL(pci_epc_get_features);
> >  
> > +/**
> > + * pci_epc_get_aux_resources() - query EPC-provided auxiliary 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 auxiliary resource queries
> > + *   * other -errno on failure
> > + */
> > +int pci_epc_get_aux_resources(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> > +			      struct pci_epc_aux_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_aux_resources)
> > +		return -EOPNOTSUPP;
> > +
> > +	mutex_lock(&epc->lock);
> > +	ret = epc->ops->get_aux_resources(epc, func_no, vfunc_no, resources,
> > +					  num_resources);
> > +	mutex_unlock(&epc->lock);
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_epc_get_aux_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 63a24ebf144c..0827650acf93 100644
> > --- a/include/linux/pci-epc.h
> > +++ b/include/linux/pci-epc.h
> > @@ -61,6 +61,51 @@ struct pci_epc_map {
> >  	void __iomem	*virt_addr;
> >  };
> >  
> > +/**
> > + * enum pci_epc_aux_resource_type - auxiliary resource type identifiers
> > + * @PCI_EPC_AUX_DMA_CTRL_MMIO: Integrated DMA controller register window (MMIO)
> > + * @PCI_EPC_AUX_DMA_CHAN_DESC: Per-channel DMA descriptor
> > + * @PCI_EPC_AUX_DOORBELL_MMIO: Doorbell MMIO, that might be outside the DMA
> > + *                             controller register window
> > + *
> > + * 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_aux_resource_type {
> > +	PCI_EPC_AUX_DMA_CTRL_MMIO,
> > +	PCI_EPC_AUX_DMA_CHAN_DESC,
> 
> I see that these resources are only used in [1], which is still in early stage.
> It'd help if you can just keep DOORBELL_MMIO resource related code in this
> series and add these resources when required.

Thanks for the suggestion.

Agree. I'll drop PCI_EPC_AUX_DMA_CTRL_MMIO and PCI_EPC_AUX_DMA_CHAN_DESC from
this series, and add them later when the consumer is in place.

Best regards,
Koichiro

> 
> - Mani
> 
> [1] https://lore.kernel.org/linux-pci/[email protected]
> 
> -- 
> மணிவண்ணன் சதாசிவம்