mfd: Add ChromeOS EC SPI driver

This uses a SPI bus to talk to the ChromeOS EC. The protocol
is defined by the EC and is fairly simple, with a length byte,
checksum, command byte and version byte (to permit easy creation
of new commands).

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/Kconfig

@@ -39,6 +39,16 @@ config MFD_CROS_EC_I2C
 	  a checksum. Failing accesses will be retried three times to
 	  improve reliability.
 
+config MFD_CROS_EC_SPI
+	tristate "ChromeOS Embedded Controller (SPI)"
+	depends on MFD_CROS_EC && SPI
+
+	---help---
+	  If you say Y here, you get support for talking to the ChromeOS EC
+	  through a SPI bus, using a byte-level protocol. Since the EC's
+	  response time cannot be guaranteed, we support ignoring
+	  'pre-amble' bytes before the response actually starts.
+
 config MFD_88PM800
 	tristate "Support Marvell 88PM800"
 	depends on I2C=y && GENERIC_HARDIRQS

drivers/mfd/Makefile

@@ -10,6 +10,7 @@ obj-$(CONFIG_MFD_SM501)		+= sm501.o
 obj-$(CONFIG_MFD_ASIC3)		+= asic3.o tmio_core.o
 obj-$(CONFIG_MFD_CROS_EC)	+= cros_ec.o
 obj-$(CONFIG_MFD_CROS_EC_I2C)	+= cros_ec_i2c.o
+obj-$(CONFIG_MFD_CROS_EC_SPI)	+= cros_ec_spi.o
 
 rtsx_pci-objs			:= rtsx_pcr.o rts5209.o rts5229.o rtl8411.o rts5227.o
 obj-$(CONFIG_MFD_RTSX_PCI)	+= rtsx_pci.o