spi: lantiq-ssc: add support for Lantiq SSC SPI controller

This driver supports the Lantiq SSC SPI controller in master
mode. This controller is found on Intel (former Lantiq) SoCs like
the Danube, Falcon, xRX200, xRX300.

The hardware uses two hardware FIFOs one for received and one for
transferred bytes. When the driver writes data into the transmit FIFO
the complete word is taken from the FIFO into a shift register. The
data from this shift register is then written to the wire. This driver
uses the interrupts signaling the status of the FIFOs and not the shift
register. It is also possible to use the interrupts for the shift
register, but they will send a signal after every word. When using the
interrupts for the shift register we get a signal when the last word is
written into the shift register and not when it is written to the wire.
After all FIFOs are empty the driver busy waits till the hardware is
not busy any more and returns the transfer status.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-lantiq-ssc.txt

+Lantiq Synchronous Serial Controller (SSC) SPI master driver
+
+Required properties:
+- compatible: "lantiq,ase-spi", "lantiq,falcon-spi", "lantiq,xrx100-spi"
+- #address-cells: see spi-bus.txt
+- #size-cells: see spi-bus.txt
+- reg: address and length of the spi master registers
+- interrupts: should contain the "spi_rx", "spi_tx" and "spi_err" interrupt.
+
+
+Optional properties:
+- clocks: spi clock phandle
+- num-cs: see spi-bus.txt, set to 8 if unset
+- base-cs: the number of the first chip select, set to 1 if unset.
+
+Example:
+
+
+spi: spi@E100800 {
+	compatible = "lantiq,xrx200-spi", "lantiq,xrx100-spi";
+	reg = <0xE100800 0x100>;
+	interrupt-parent = <&icu0>;
+	interrupts = <22 23 24>;
+	interrupt-names = "spi_rx", "spi_tx", "spi_err";
+	#address-cells = <1>;
+	#size-cells = <1>;
+	num-cs = <6>;
+	base-cs = <1>;
+};

drivers/spi/Kconfig

@@ -415,6 +415,14 @@ config SPI_NUC900
 	help
 	  SPI driver for Nuvoton NUC900 series ARM SoCs
 
+config SPI_LANTIQ_SSC
+	tristate "Lantiq SSC SPI controller"
+	depends on LANTIQ
+	help
+	  This driver supports the Lantiq SSC SPI controller in master
+	  mode. This controller is found on Intel (former Lantiq) SoCs like
+	  the Danube, Falcon, xRX200, xRX300.
+
 config SPI_OC_TINY
 	tristate "OpenCores tiny SPI"
 	depends on GPIOLIB || COMPILE_TEST

drivers/spi/Makefile

@@ -49,6 +49,7 @@ obj-$(CONFIG_SPI_FSL_SPI)		+= spi-fsl-spi.o
 obj-$(CONFIG_SPI_GPIO)			+= spi-gpio.o
 obj-$(CONFIG_SPI_IMG_SPFI)		+= spi-img-spfi.o
 obj-$(CONFIG_SPI_IMX)			+= spi-imx.o
+obj-$(CONFIG_SPI_LANTIQ_SSC)		+= spi-lantiq-ssc.o
 obj-$(CONFIG_SPI_JCORE)			+= spi-jcore.o
 obj-$(CONFIG_SPI_LM70_LLP)		+= spi-lm70llp.o
 obj-$(CONFIG_SPI_LP8841_RTC)		+= spi-lp8841-rtc.o