spi: cadence: add support for Cadence XSPI controller

This patch adds driver for Cadence's XSPI controller.
It supports 3 work modes.
1. ACMD (auto command) work mode
    ACMD name is because it uses auto command engine in the controller.
    It further has 2 modes PIO and CDMA (command DMA).
    The CDMA work mode is dedicated for high-performance application
    where very low software overhead is required. In this mode the
    Command Engine is programmed by the series of linked descriptors
    stored in system memory. These descriptors provide commands to execute
    and store status information for finished commands.
    The PIO mode work mode is dedicated for single operation where
    constructing a linked list of descriptors would require too
    much effort.
2. STIG (Software Triggered Instruction Generator) work mode
    In STIG mode, controller sends low-level instructions to memory.
    Each instruction is 128-bit width. There is special instruction
    DataSequence which carries information about data phase.
    Driver uses Slave DMA interface to transfer data as only this
    interface can be used in STIG work mode.
3. Direct work mode
    This work mode allows sending data without invoking any command through
    the slave interface.
Currently only STIG work mode is enabled, remaining work modes will
be added later.

Signed-off-by: Konrad Kociolek <konrad@cadence.com>
Signed-off-by: Jayshri Pawar <jpawar@cadence.com>
Signed-off-by: Parshuram Thombare <pthombar@cadence.com>
Acked-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/1632038734-23999-1-git-send-email-pthombar@cadence.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/Kconfig

@@ -228,6 +228,18 @@ config SPI_CADENCE_QUADSPI
 	  device with a Cadence QSPI controller and want to access the
 	  Flash as an MTD device.
 
+config SPI_CADENCE_XSPI
+	tristate "Cadence XSPI controller"
+	depends on (OF || COMPILE_TEST) && HAS_IOMEM
+	depends on SPI_MEM
+	help
+	  Enable support for the Cadence XSPI Flash controller.
+
+	  Cadence XSPI is a specialized controller for connecting an SPI
+	  Flash over upto 8bit wide bus. Enable this option if you have a
+	  device with a Cadence XSPI controller and want to access the
+	  Flash as an MTD device.
+
 config SPI_CLPS711X
 	tristate "CLPS711X host SPI controller"
 	depends on ARCH_CLPS711X || COMPILE_TEST

drivers/spi/Makefile

@@ -34,6 +34,7 @@ obj-$(CONFIG_SPI_BITBANG)		+= spi-bitbang.o
 obj-$(CONFIG_SPI_BUTTERFLY)		+= spi-butterfly.o
 obj-$(CONFIG_SPI_CADENCE)		+= spi-cadence.o
 obj-$(CONFIG_SPI_CADENCE_QUADSPI)	+= spi-cadence-quadspi.o
+obj-$(CONFIG_SPI_CADENCE_XSPI)		+= spi-cadence-xspi.o
 obj-$(CONFIG_SPI_CLPS711X)		+= spi-clps711x.o
 obj-$(CONFIG_SPI_COLDFIRE_QSPI)		+= spi-coldfire-qspi.o
 obj-$(CONFIG_SPI_DAVINCI)		+= spi-davinci.o