staging: add driver for Xilinx AXI-Stream FIFO v4.1 IP core

This IP core has read and write AXI-Stream FIFOs, the contents of which can
be accessed from the AXI4 memory-mapped interface. This is useful for
transferring data from a processor into the FPGA fabric. The driver creates
a character device that can be read/written to with standard
open/read/write/close.

See Xilinx PG080 document for IP details.

https://www.xilinx.com/support/documentation/ip_documentation/axi_fifo_mm_s/v4_1/pg080-axi-fifo-mm-s.pdf

The driver currently supports only store-forward mode with a 32-bit
AXI4 Lite interface. DOES NOT support:
        - cut-through mode
        - AXI4 (non-lite)

Signed-off-by: Jacob Feder <jacobsfeder@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/Kconfig

@@ -124,4 +124,6 @@ source "drivers/staging/mt7621-dts/Kconfig"
 
 source "drivers/staging/gasket/Kconfig"
 
+source "drivers/staging/axis-fifo/Kconfig"
+
 endif # STAGING

drivers/staging/Makefile

@@ -53,3 +53,4 @@ obj-$(CONFIG_SOC_MT7621)	+= mt7621-mmc/
 obj-$(CONFIG_SOC_MT7621)	+= mt7621-eth/
 obj-$(CONFIG_SOC_MT7621)	+= mt7621-dts/
 obj-$(CONFIG_STAGING_GASKET_FRAMEWORK)	+= gasket/
+obj-$(CONFIG_XIL_AXIS_FIFO)	+= axis-fifo/

drivers/staging/axis-fifo/Kconfig

@@ -0,0 +1,9 @@
+#
+# "Xilinx AXI-Stream FIFO IP core driver"
+#
+config XIL_AXIS_FIFO
+	tristate "Xilinx AXI-Stream FIFO IP core driver"
+	default n
+	help
+	  This adds support for the Xilinx AXI-Stream
+	  FIFO IP core driver.

drivers/staging/axis-fifo/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_XIL_AXIS_FIFO) += axis-fifo.o