NTB: Add support for EPF PCI Non-Transparent Bridge

Add support for EPF PCI Non-Transparent Bridge (NTB) devices.  This driver
is platform independent and may be used by any platform that has multiple
PCI endpoint instances configured using the pci-epf-ntb driver.  The driver
connnects to the standard NTB subsystem interface. The EPF NTB device has a
configurable number of memory windows (max 4), a configurable number of
doorbells (max 32), and a configurable number of scratch-pad registers.

Link: https://lore.kernel.org/r/20210201195809.7342-16-kishon@ti.com
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>

drivers/ntb/hw/Kconfig

@@ -2,4 +2,5 @@
 source "drivers/ntb/hw/amd/Kconfig"
 source "drivers/ntb/hw/idt/Kconfig"
 source "drivers/ntb/hw/intel/Kconfig"
+source "drivers/ntb/hw/epf/Kconfig"
 source "drivers/ntb/hw/mscc/Kconfig"

drivers/ntb/hw/Makefile

@@ -2,4 +2,5 @@
 obj-$(CONFIG_NTB_AMD)	+= amd/
 obj-$(CONFIG_NTB_IDT)	+= idt/
 obj-$(CONFIG_NTB_INTEL)	+= intel/
+obj-$(CONFIG_NTB_EPF)	+= epf/
 obj-$(CONFIG_NTB_SWITCHTEC) += mscc/

drivers/ntb/hw/epf/Kconfig

@@ -0,0 +1,6 @@
+config NTB_EPF
+	tristate "Generic EPF Non-Transparent Bridge support"
+	depends on m
+	help
+	  This driver supports EPF NTB on configurable endpoint.
+	  If unsure, say N.

drivers/ntb/hw/epf/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_NTB_EPF) += ntb_hw_epf.o