char: xillybus: Add driver for XillyUSB (Xillybus variant for USB)

The XillyUSB driver is the USB variant for the Xillybus FPGA IP core.
Even though it presents a nearly identical API on the FPGA and host,
it's almost a complete rewrite of the driver: The framework for exchanging
data on a USB bus is fundamentally different from doing the same with a
PCIe interface, which leaves very little in common between the existing
driver and the new one for XillyUSB.
Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Link: https://lore.kernel.org/r/20210526100311.56327-3-eli.billauer@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/xillybus/Kconfig

@@ -36,3 +36,17 @@ config XILLYBUS_OF
 	  system, say M. The module will be called xillybus_of.
 
 endif # if XILLYBUS
+
+# XILLYUSB doesn't depend on XILLYBUS
+
+config XILLYUSB
+	tristate "XillyUSB: Xillybus generic FPGA interface for USB"
+	depends on USB
+	select CRC32
+	select XILLYBUS_CLASS
+	help
+	  XillyUSB is the Xillybus variant which uses USB for communicating
+	  with the FPGA.
+
+	  Set to M if you want Xillybus to use USB for communicating with
+	  the FPGA. The module will be called xillyusb.

drivers/char/xillybus/Makefile

@@ -7,3 +7,4 @@ obj-$(CONFIG_XILLYBUS_CLASS)	+= xillybus_class.o
 obj-$(CONFIG_XILLYBUS)		+= xillybus_core.o
 obj-$(CONFIG_XILLYBUS_PCIE)	+= xillybus_pcie.o
 obj-$(CONFIG_XILLYBUS_OF)	+= xillybus_of.o
+obj-$(CONFIG_XILLYUSB)		+= xillyusb.o