misc: gehc-achc: new driver

General Electric Healthcare's PPD has a secondary processor from
NXP's Kinetis K20 series. That device has two SPI chip selects:

The main interface's behaviour depends on the loaded firmware
and is currently unused.

The secondary interface can be used to update the firmware using
EzPort protocol. This is implemented by this driver using the
kernel's firmware API. The firmware is being flashed into
non-volatile flash memory, so it is enough to flash it once
and not on every boot. Flashing will wear the flash memory
(it has a life time of at least 10k programming cycles). At
the same time only occasional FW updates are expected (like e.g.
a BIOS update). Thus the firmware update is triggered via sysfs
instead of doing it in the driver's probe routine like many
other drivers.
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20210802172309.164365-4-sebastian.reichel@collabora.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-driver-ge-achc

+What:		/sys/bus/spi/<dev>/update_firmware
+Date:		Jul 2021
+Contact:	sebastian.reichel@collabora.com
+Description:	Write 1 to this file to update the ACHC microcontroller
+		firmware via the EzPort interface. For this the kernel
+		will load "achc.bin" via the firmware API (so usually
+		from /lib/firmware). The write will block until the FW
+		has either been flashed successfully or an error occured.
+
+What:		/sys/bus/spi/<dev>/reset
+Date:		Jul 2021
+Contact:	sebastian.reichel@collabora.com
+Description:	This file represents the microcontroller's reset line.
+                1 means the reset line is asserted, 0 means it's not
+		asserted. The file is read and writable.

drivers/misc/Kconfig

@@ -208,6 +208,18 @@ config CS5535_CLOCK_EVENT_SRC
 	  MFGPTs have a better resolution and max interval than the
 	  generic PIT, and are suitable for use as high-res timers.
 
+config GEHC_ACHC
+	tristate "GEHC ACHC support"
+	depends on SPI && SYSFS
+	depends on SOC_IMX53 || COMPILE_TEST
+	select FW_LOADER
+	help
+	  Support for GE ACHC microcontroller, that is part of the GE
+	  PPD device.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called gehc-achc.
+
 config HP_ILO
 	tristate "Channel interface driver for the HP iLO processor"
 	depends on PCI

drivers/misc/Makefile

@@ -24,6 +24,7 @@ obj-$(CONFIG_KGDB_TESTS)	+= kgdbts.o
 obj-$(CONFIG_SGI_XP)		+= sgi-xp/
 obj-$(CONFIG_SGI_GRU)		+= sgi-gru/
 obj-$(CONFIG_CS5535_MFGPT)	+= cs5535-mfgpt.o
+obj-$(CONFIG_GEHC_ACHC)		+= gehc-achc.o
 obj-$(CONFIG_HP_ILO)		+= hpilo.o
 obj-$(CONFIG_APDS9802ALS)	+= apds9802als.o
 obj-$(CONFIG_ISL29003)		+= isl29003.o

drivers/spi/spidev.c

@@ -677,7 +677,6 @@ static struct class *spidev_class;
 static const struct of_device_id spidev_dt_ids[] = {
 	{ .compatible = "rohm,dh2228fv" },
 	{ .compatible = "lineartechnology,ltc2488" },
-	{ .compatible = "ge,achc" },
 	{ .compatible = "semtech,sx1301" },
 	{ .compatible = "lwn,bk4" },
 	{ .compatible = "dh,dhcom-board" },