Add helper function pci_epf_msi_domain_get_msi_rid() to convert EP device
id to msi domain's request ID to pave the road to support RC-to-EP doorbell
with platform MSI controller.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
change from v12 to v13
- new patch
---
 drivers/pci/endpoint/Makefile     |  2 +-
 drivers/pci/endpoint/pci-ep-msi.c | 36 ++++++++++++++++++++++++++++++++++++
 include/linux/pci-ep-msi.h        | 21 +++++++++++++++++++++
 3 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/endpoint/Makefile b/drivers/pci/endpoint/Makefile
index 95b2fe47e3b06..a1ccce440c2c5 100644
--- a/drivers/pci/endpoint/Makefile
+++ b/drivers/pci/endpoint/Makefile
@@ -5,4 +5,4 @@
 
 obj-$(CONFIG_PCI_ENDPOINT_CONFIGFS)	+= pci-ep-cfs.o
 obj-$(CONFIG_PCI_ENDPOINT)		+= pci-epc-core.o pci-epf-core.o\
-					   pci-epc-mem.o functions/
+					   pci-epc-mem.o pci-ep-msi.o functions/
diff --git a/drivers/pci/endpoint/pci-ep-msi.c b/drivers/pci/endpoint/pci-ep-msi.c
new file mode 100644
index 0000000000000..7aedc1cafbd14
--- /dev/null
+++ b/drivers/pci/endpoint/pci-ep-msi.c
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * PCI Endpoint *Controller* (EPC) MSI library
+ *
+ * Copyright (C) 2024 NXP
+ * Author: Frank Li <Frank.Li@nxp.com>
+ */
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/msi.h>
+#include <linux/of_irq.h>
+#include <linux/pci-epc.h>
+#include <linux/pci-epf.h>
+#include <linux/pci-ep-cfs.h>
+#include <linux/pci-ep-msi.h>
+#include <linux/slab.h>
+
+int pci_epf_msi_domain_get_msi_rid(struct device *dev, u32 *rid)
+{
+	struct pci_epf *epf = to_pci_epf(dev);
+	struct pci_epc *epc = epf->epc;
+
+	if (!rid)
+		return -EINVAL;
+
+	/*
+	 * PCI Endpoint device ID can't full reuse PCI's BDF, BUS number is
+	 * Root Complex Bus number, which is no means for EP side. Move func_no
+	 * as low 3 bits to partially match PCI's BDF.
+	 */
+	*rid = of_msi_map_id(epc->dev.parent, NULL, (epf->func_no & 0x7) | (epf->vfunc_no << 3));
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pci_epf_msi_domain_get_msi_rid);
diff --git a/include/linux/pci-ep-msi.h b/include/linux/pci-ep-msi.h
new file mode 100644
index 0000000000000..75236867426a4
--- /dev/null
+++ b/include/linux/pci-ep-msi.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * PCI Endpoint *Function* side MSI header file
+ *
+ * Copyright (C) 2024 NXP
+ * Author: Frank Li <Frank.Li@nxp.com>
+ */
+
+#ifndef __PCI_EP_MSI__
+#define __PCI_EP_MSI__
+
+#ifdef CONFIG_PCI_ENDPOINT
+int pci_epf_msi_domain_get_msi_rid(struct device *dev, u32 *rid);
+#else
+static inline int pci_epf_msi_domain_get_msi_rid(struct device *dev, u32 *rid)
+{
+	return -EINVAL;
+}
+#endif
+
+#endif /* __PCI_EP_MSI__ */

-- 
2.34.1