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

[Koichiro Den]

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@xxxxxxxxxxxxx>
---
 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
-- 
2.51.0