spi/qspi: Add qspi flash controller

The patch add basic support for the quad spi controller.

QSPI is a kind of spi module that allows single,
dual and quad read access to external spi devices. The module
has a memory mapped interface which provide direct interface
for accessing data form external spi devices.

The patch will configure controller clocks, device control
register and for defining low level transfer apis which
will be used by the spi framework to transfer data to
the slave spi device(flash in this case).

Test details:
-------------
Tested this on dra7 board.
Test1: Ran mtd_stesstest for 40000 iterations.
   - All iterations went through without failure.
Test2: Use mtd utilities:
  - flash_erase to erase the flash device
  - mtd_debug read to read data back.
  - mtd_debug write to write to the data flash.
 diff between the write and read data shows zero.

Acked-by: Felipe Balbi<balbi@ti.com>
Reviewed-by: Felipe Balbi<balbi@ti.com>
Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

Documentation/devicetree/bindings/spi/ti_qspi.txt

+TI QSPI controller.
+
+Required properties:
+- compatible : should be "ti,dra7xxx-qspi".
+- reg: Should contain QSPI registers location and length.
+- #address-cells, #size-cells : Must be present if the device has sub-nodes
+- ti,hwmods: Name of the hwmod associated to the QSPI
+
+Recommended properties:
+- spi-max-frequency: Definition as per
+                     Documentation/devicetree/bindings/spi/spi-bus.txt
+
+Example:
+
+qspi: qspi@4b300000 {
+	compatible = "ti,dra7xxx-qspi";
+	reg = <0x4b300000 0x100>;
+	#address-cells = <1>;
+	#size-cells = <0>;
+	spi-max-frequency = <25000000>;
+	ti,hwmods = "qspi";
+};

drivers/spi/Kconfig

@@ -285,6 +285,14 @@ config SPI_OMAP24XX
 	  SPI master controller for OMAP24XX and later Multichannel SPI
 	  (McSPI) modules.
 
+config SPI_TI_QSPI
+	tristate "DRA7xxx QSPI controller support"
+	depends on ARCH_OMAP2PLUS || COMPILE_TEST
+	help
+	  QSPI master controller for DRA7xxx used for flash devices.
+	  This device supports single, dual and quad read support, while
+	  it only supports single write mode.
+
 config SPI_OMAP_100K
 	tristate "OMAP SPI 100K"
 	depends on ARCH_OMAP850 || ARCH_OMAP730

drivers/spi/Makefile

@@ -46,6 +46,7 @@ obj-$(CONFIG_SPI_OCTEON)		+= spi-octeon.o
 obj-$(CONFIG_SPI_OMAP_UWIRE)		+= spi-omap-uwire.o
 obj-$(CONFIG_SPI_OMAP_100K)		+= spi-omap-100k.o
 obj-$(CONFIG_SPI_OMAP24XX)		+= spi-omap2-mcspi.o
+obj-$(CONFIG_SPI_TI_QSPI)		+= spi-ti-qspi.o
 obj-$(CONFIG_SPI_ORION)			+= spi-orion.o
 obj-$(CONFIG_SPI_PL022)			+= spi-pl022.o
 obj-$(CONFIG_SPI_PPC4xx)		+= spi-ppc4xx.o