PCI: endpoint: Add pci_epf_align_inbound_addr() helper for inbound address alignment

Add pci_epf_align_inbound_addr() to align the inbound addresses according
to PCI BAR alignment requirements. The aligned base address and offset are
returned via 'base' and 'off' parameters.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
[mani: reworded kernel-doc and commit message]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Niklas Cassel <cassel@kernel.org>
Link: https://patch.msgid.link/20250710-ep-msi-v21-5-57683fc7fb25@nxp.com

Author: nxpfrankli

drivers/pci/endpoint/pci-epf-core.c

@@ -477,6 +477,44 @@ struct pci_epf *pci_epf_create(const char *name)
 }
 EXPORT_SYMBOL_GPL(pci_epf_create);
 
+/**
+ * pci_epf_align_inbound_addr() - Align the given address based on the BAR
+ *				  alignment requirement
+ * @epf: the EPF device
+ * @addr: inbound address to be aligned
+ * @bar: the BAR number corresponding to the given addr
+ * @base: base address matching the @bar alignment requirement
+ * @off: offset to be added to the @base address
+ *
+ * Helper function to align input @addr based on BAR's alignment requirement.
+ * The aligned base address and offset are returned via @base and @off.
+ *
+ * NOTE: The pci_epf_alloc_space() function already accounts for alignment.
+ * This API is primarily intended for use with other memory regions not
+ * allocated by pci_epf_alloc_space(), such as peripheral register spaces or
+ * the message address of a platform MSI controller.
+ *
+ * Return: 0 on success, errno otherwise.
+ */
+int pci_epf_align_inbound_addr(struct pci_epf *epf, enum pci_barno bar,
+			       u64 addr, dma_addr_t *base, size_t *off)
+{
+	/*
+	 * Most EP controllers require the BAR start address to be aligned to
+	 * the BAR size, because they mask off the lower bits.
+	 *
+	 * Alignment to BAR size also works for controllers that support
+	 * unaligned addresses.
+	 */
+	u64 align = epf->bar[bar].size;
+
+	*base = round_down(addr, align);
+	*off = addr & (align - 1);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pci_epf_align_inbound_addr);
+
 static void pci_epf_dev_release(struct device *dev)
 {
 	struct pci_epf *epf = to_pci_epf(dev);

include/linux/pci-epf.h

@@ -241,6 +241,9 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
 			  enum pci_epc_interface_type type);
 void pci_epf_free_space(struct pci_epf *epf, void *addr, enum pci_barno bar,
 			enum pci_epc_interface_type type);
+
+int pci_epf_align_inbound_addr(struct pci_epf *epf, enum pci_barno bar,
+			       u64 addr, dma_addr_t *base, size_t *off);
 int pci_epf_bind(struct pci_epf *epf);
 void pci_epf_unbind(struct pci_epf *epf);
 int pci_epf_add_vepf(struct pci_epf *epf_pf, struct pci_epf *epf_vf);