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 <den@valinux.co.jp>
---
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)
+{
+ 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
--
2.51.0On 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 <den@valinux.co.jp>
> ---
> 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
...
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
>
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 <den@valinux.co.jp>
> > ---
> > 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
> >
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