Re: [PATCH 07/15] PCI: endpoint: Add EPC DMA channel delegation hooks

On Thu, Mar 12, 2026 at 04:39:34PM -0400, Frank Li wrote:
> On Fri, Mar 13, 2026 at 01:49:57AM +0900, Koichiro Den wrote:
> > Add EPC ops and core wrappers to delegate and undelegate controller-owned
> > DMA channels.
> >
> > The exported DMA helper needs more than a passive "delegated" bitmap:
> > it must be able to reserve channels away from local users, let the
> > backend perform controller-specific setup (e.g. prevent the EP from
> > racing to ack the completion interrupt for delegated channels), and
> > later hand the channels back as a matched lifetime operation.
> >
> > Signed-off-by: Koichiro Den <[email protected]>
> > ---
> >  drivers/pci/endpoint/pci-epc-core.c | 84 +++++++++++++++++++++++++++++
> >  include/linux/pci-epc.h             | 19 +++++++
> >  2 files changed, 103 insertions(+)
> >
> > diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
> > index dc6d6ab4ea1e..892f7ccbd236 100644
> > --- a/drivers/pci/endpoint/pci-epc-core.c
> > +++ b/drivers/pci/endpoint/pci-epc-core.c
> > @@ -197,6 +197,90 @@ int pci_epc_get_aux_resources(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> >  }
> >  EXPORT_SYMBOL_GPL(pci_epc_get_aux_resources);
> >
> > +/**
> > + * pci_epc_delegate_dma_channels() - reserve EPC-owned DMA channels
> > + * @epc: EPC device
> > + * @func_no: function number
> > + * @vfunc_no: virtual function number
> > + * @dir: DMA channel direction
> > + * @req_chans: number of channels requested
> > + * @chan_ids: output array of delegated channel IDs
> > + * @max_chans: capacity of @chan_ids in entries
> > + *
> > + * Return:
> > + *   * > 0: number of channels delegated
> > + *   * -EOPNOTSUPP: backend does not support DMA delegation
> > + *   * other -errno on failure
> > + */
> > +int pci_epc_delegate_dma_channels(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> > +				  enum pci_epc_aux_dma_dir dir,
> > +				  u32 req_chans, int *chan_ids, u32 max_chans)
> 
> Use bit mask should be simple, bit 0 for channel 0, bit 1 for channel 1

Thanks for the suggestion. I'll rework this part when respinning to simplify the
interface.

I also posted a follow-up to clarify the overall direction of this series:
https://lore.kernel.org/linux-pci/sn67hi7kljh7cgmgodatb3naz2astlaklqfobdbxyyzgoohxqb@4nnetbhqwba4/

So far there has been no feedback beyond yours, so I'll wait a bit to see if
there are further comments on this series.

Thank you for revieweing,
Koichiro

> ...
> 
> Frank
> > +{
> > +	int ret;
> > +
> > +	if (!epc || !epc->ops)
> > +		return -EINVAL;
> > +
> > +	if (!pci_epc_function_is_valid(epc, func_no, vfunc_no))
> > +		return -EINVAL;
> > +
> > +	if (!req_chans || !chan_ids || !max_chans)
> > +		return -EINVAL;
> > +
> > +	if (!epc->ops->delegate_dma_channels)
> > +		return -EOPNOTSUPP;
> > +
> > +	mutex_lock(&epc->lock);
> > +	ret = epc->ops->delegate_dma_channels(epc, func_no, vfunc_no, dir,
> > +					      req_chans, chan_ids, max_chans);
> > +	mutex_unlock(&epc->lock);
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_epc_delegate_dma_channels);
> > +
> > +/**
> > + * pci_epc_undelegate_dma_channels() - release previously delegated channels
> > + * @epc: EPC device
> > + * @func_no: function number
> > + * @vfunc_no: virtual function number
> > + * @dir: DMA channel direction
> > + * @chan_ids: array of delegated channel IDs
> > + * @num_chans: number of entries in @chan_ids
> > + *
> > + * Return: 0 on success, negative errno otherwise.
> > + */
> > +int pci_epc_undelegate_dma_channels(struct pci_epc *epc, u8 func_no,
> > +				    u8 vfunc_no,
> > +				    enum pci_epc_aux_dma_dir dir,
> > +				    const int *chan_ids, u32 num_chans)
> > +{
> > +	int ret;
> > +
> > +	if (!epc || !epc->ops)
> > +		return -EINVAL;
> > +
> > +	if (!pci_epc_function_is_valid(epc, func_no, vfunc_no))
> > +		return -EINVAL;
> > +
> > +	if (!num_chans)
> > +		return 0;
> > +
> > +	if (!chan_ids)
> > +		return -EINVAL;
> > +
> > +	if (!epc->ops->undelegate_dma_channels)
> > +		return -EOPNOTSUPP;
> > +
> > +	mutex_lock(&epc->lock);
> > +	ret = epc->ops->undelegate_dma_channels(epc, func_no, vfunc_no, dir,
> > +						chan_ids, num_chans);
> > +	mutex_unlock(&epc->lock);
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_epc_undelegate_dma_channels);
> > +
> >  /**
> >   * 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 7dd2e4d5d952..db8623b84c56 100644
> > --- a/include/linux/pci-epc.h
> > +++ b/include/linux/pci-epc.h
> > @@ -142,6 +142,8 @@ struct pci_epc_aux_resource {
> >   * @stop: ops to stop the PCI link
> >   * @get_features: ops to get the features supported by the EPC
> >   * @get_aux_resources: ops to retrieve controller-owned auxiliary resources
> > + * @delegate_dma_channels: reserve controller-owned DMA channels for peer use
> > + * @undelegate_dma_channels: release previously delegated DMA channels
> >   * @owner: the module owner containing the ops
> >   */
> >  struct pci_epc_ops {
> > @@ -176,6 +178,16 @@ struct pci_epc_ops {
> >  	int	(*get_aux_resources)(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> >  				     struct pci_epc_aux_resource *resources,
> >  				     int num_resources);
> > +	int	(*delegate_dma_channels)(struct pci_epc *epc, u8 func_no,
> > +					 u8 vfunc_no,
> > +					 enum pci_epc_aux_dma_dir dir,
> > +					 u32 req_chans, int *chan_ids,
> > +					 u32 max_chans);
> > +	int	(*undelegate_dma_channels)(struct pci_epc *epc, u8 func_no,
> > +					   u8 vfunc_no,
> > +					   enum pci_epc_aux_dma_dir dir,
> > +					   const int *chan_ids,
> > +					   u32 num_chans);
> >  	struct module *owner;
> >  };
> >
> > @@ -403,6 +415,13 @@ const struct pci_epc_features *pci_epc_get_features(struct pci_epc *epc,
> >  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 pci_epc_delegate_dma_channels(struct pci_epc *epc, u8 func_no,
> > +				  u8 vfunc_no, enum pci_epc_aux_dma_dir dir,
> > +				  u32 req_chans, int *chan_ids, u32 max_chans);
> > +int pci_epc_undelegate_dma_channels(struct pci_epc *epc, u8 func_no,
> > +				    u8 vfunc_no,
> > +				    enum pci_epc_aux_dma_dir dir,
> > +				    const int *chan_ids, u32 num_chans);
> >  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
> >