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_count() / pci_epc_get_aux_resources() and
the corresponding pci_epc_ops callbacks. The count helper returns the
number of available resources, 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 <mani@kernel.org>
Suggested-by: Frank Li <Frank.li@nxp.com>
Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
Changes in v13:
  - Renamed pci_epc_count_aux_resources() to
    pci_epc_get_aux_resources_count() and have it return the count
    directly.
  - Updated commit message accordingly.

 drivers/pci/endpoint/pci-epc-core.c | 80 +++++++++++++++++++++++++++++
 include/linux/pci-epc.h             | 54 +++++++++++++++++++
 2 files changed, 134 insertions(+)

diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
index 6c3c58185fc5..efcd0f8b33bc 100644
--- a/drivers/pci/endpoint/pci-epc-core.c
+++ b/drivers/pci/endpoint/pci-epc-core.c
@@ -156,6 +156,86 @@ 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_count() - get the number of EPC-provided auxiliary resources
+ * @epc: EPC device
+ * @func_no: function number
+ * @vfunc_no: virtual function number
+ *
+ * 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: the number of available resources on success, -EOPNOTSUPP if the
+ * backend does not support auxiliary resource queries, or another -errno on
+ * failure.
+ */
+int pci_epc_get_aux_resources_count(struct pci_epc *epc, u8 func_no,
+				    u8 vfunc_no)
+{
+	int count;
+
+	if (!epc || !epc->ops)
+		return -EINVAL;
+
+	if (!pci_epc_function_is_valid(epc, func_no, vfunc_no))
+		return -EINVAL;
+
+	if (!epc->ops->get_aux_resources_count)
+		return -EOPNOTSUPP;
+
+	mutex_lock(&epc->lock);
+	count = epc->ops->get_aux_resources_count(epc, func_no,
+					          vfunc_no);
+	mutex_unlock(&epc->lock);
+
+	return count;
+}
+EXPORT_SYMBOL_GPL(pci_epc_get_aux_resources_count);
+
+/**
+ * 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
+ * @num_resources: size of @resources array in entries
+ *
+ * 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 on success, -EOPNOTSUPP if the backend does not support auxiliary
+ * resource queries, or another -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 (!resources || num_resources <= 0)
+		return -EINVAL;
+
+	if (!epc || !epc->ops)
+		return -EINVAL;
+
+	if (!pci_epc_function_is_valid(epc, func_no, vfunc_no))
+		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 1eca1264815b..2f2848542726 100644
--- a/include/linux/pci-epc.h
+++ b/include/linux/pci-epc.h
@@ -61,6 +61,47 @@ struct pci_epc_map {
 	void __iomem	*virt_addr;
 };
 
+/**
+ * enum pci_epc_aux_resource_type - auxiliary resource type identifiers
+ * @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_DOORBELL_MMIO,
+};
+
+/**
+ * struct pci_epc_aux_resource - a physical auxiliary resource that may be
+ *                               exposed for peer use
+ * @type:       resource type, see enum pci_epc_aux_resource_type
+ * @phys_addr:  physical base address of the resource
+ * @size:       size of the resource in bytes
+ * @bar:        BAR number where this resource is already exposed to the RC
+ *              (NO_BAR if not)
+ * @bar_offset: offset within @bar where the resource starts (valid iff
+ *              @bar != NO_BAR)
+ * @u:          type-specific metadata
+ */
+struct pci_epc_aux_resource {
+	enum pci_epc_aux_resource_type type;
+	phys_addr_t phys_addr;
+	resource_size_t size;
+	enum pci_barno bar;
+	resource_size_t bar_offset;
+
+	union {
+		/* PCI_EPC_AUX_DOORBELL_MMIO */
+		struct {
+			int irq; /* IRQ number for the doorbell handler */
+			u32 data; /* write value to ring the doorbell */
+		} db_mmio;
+	} u;
+};
+
 /**
  * struct pci_epc_ops - set of function pointers for performing EPC operations
  * @write_header: ops to populate configuration space header
@@ -84,6 +125,9 @@ struct pci_epc_map {
  * @start: ops to start the PCI link
  * @stop: ops to stop the PCI link
  * @get_features: ops to get the features supported by the EPC
+ * @get_aux_resources_count: ops to get the number of controller-owned
+ *                           auxiliary resources
+ * @get_aux_resources: ops to retrieve controller-owned auxiliary resources
  * @owner: the module owner containing the ops
  */
 struct pci_epc_ops {
@@ -115,6 +159,11 @@ struct pci_epc_ops {
 	void	(*stop)(struct pci_epc *epc);
 	const struct pci_epc_features* (*get_features)(struct pci_epc *epc,
 						       u8 func_no, u8 vfunc_no);
+	int	(*get_aux_resources_count)(struct pci_epc *epc, u8 func_no,
+				       u8 vfunc_no);
+	int	(*get_aux_resources)(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
+				     struct pci_epc_aux_resource *resources,
+				     int num_resources);
 	struct module *owner;
 };
 
@@ -343,6 +392,11 @@ int pci_epc_start(struct pci_epc *epc);
 void pci_epc_stop(struct pci_epc *epc);
 const struct pci_epc_features *pci_epc_get_features(struct pci_epc *epc,
 						    u8 func_no, u8 vfunc_no);
+int pci_epc_get_aux_resources_count(struct pci_epc *epc, u8 func_no,
+				    u8 vfunc_no);
+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);
 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