PCI: endpoint: Add PCI Endpoint function driver for MHI bus

Add PCI Endpoint driver for the Qualcomm MHI (Modem Host Interface) bus.

The driver implements the MHI function over PCI in the endpoint device such
as SDX55 modem. The MHI endpoint function driver acts as a controller
driver for the MHI Endpoint stack and carries out all PCI related
functionality.

Link: https://lore.kernel.org/r/20230602114756.36586-9-manivannan.sadhasivam@linaro.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kishon Vijay Abraham I <kishon@kernel.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

drivers/pci/endpoint/functions/Kconfig

@@ -37,3 +37,13 @@ config PCI_EPF_VNTB
 	  between PCI Root Port and PCIe Endpoint.
 
 	  If in doubt, say "N" to disable Endpoint NTB driver.
+
+config PCI_EPF_MHI
+	tristate "PCI Endpoint driver for MHI bus"
+	depends on PCI_ENDPOINT && MHI_BUS_EP
+	help
+	   Enable this configuration option to enable the PCI Endpoint
+	   driver for Modem Host Interface (MHI) bus in Qualcomm Endpoint
+	   devices such as SDX55.
+
+	   If in doubt, say "N" to disable Endpoint driver for MHI bus.

drivers/pci/endpoint/functions/Makefile

@@ -6,3 +6,4 @@
 obj-$(CONFIG_PCI_EPF_TEST)		+= pci-epf-test.o
 obj-$(CONFIG_PCI_EPF_NTB)		+= pci-epf-ntb.o
 obj-$(CONFIG_PCI_EPF_VNTB) 		+= pci-epf-vntb.o
+obj-$(CONFIG_PCI_EPF_MHI)		+= pci-epf-mhi.o