WIP: HID: transport: spi: add Apple SPI transport

Keyboard and trackpad of Apple Sillicon SoCs (M1, M1 Pro/Max) laptops
are are HID devices connected via SPI.

This is the same protocol as implemented by applespi.c. It was not
noticed that protocol is a transport for HID. Adding support for ACPI
based Intel MacBooks will be done in a separate commit.

How HID is mapped in this protocol is not yet fully understood.

Microsoft has a specification for HID over SPI [1] incompatible with the
transport protocol used by Apple.

[1] https://docs.microsoft.com/en-us/windows-hardware/drivers/hid/hid-over-spi

Signed-off-by: Janne Grunau <j@jannau.net>

Author: jannau

drivers/hid/Kconfig

@@ -1369,4 +1369,6 @@ source "drivers/hid/amd-sfh-hid/Kconfig"
 
 source "drivers/hid/surface-hid/Kconfig"
 
+source "drivers/hid/spi-hid/Kconfig"
+
 endif # HID_SUPPORT

drivers/hid/Makefile

@@ -169,3 +169,5 @@ obj-$(INTEL_ISH_FIRMWARE_DOWNLOADER)	+= intel-ish-hid/
 obj-$(CONFIG_AMD_SFH_HID)       += amd-sfh-hid/
 
 obj-$(CONFIG_SURFACE_HID_CORE)  += surface-hid/
+
+obj-$(CONFIG_SPI_HID_APPLE_CORE)	+= spi-hid/

drivers/hid/spi-hid/Kconfig

@@ -0,0 +1,26 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menu "SPI HID support"
+	depends on SPI
+
+config SPI_HID_APPLE_OF
+	tristate "HID over SPI transport layer for Apple Silicon SoCs"
+	default ARCH_APPLE
+	depends on SPI && INPUT && OF
+	help
+	  Say Y here if you use Apple Silicon based laptop. The keyboard and
+	  touchpad are HID based devices connected via SPI.
+
+	  If unsure, say N.
+
+	  This support is also available as a module.  If so, the module
+	  will be called spi-hid-apple-of. It will also build/depend on the
+	  module spi-hid-apple.
+
+endmenu
+
+config SPI_HID_APPLE_CORE
+	tristate
+	default y if SPI_HID_APPLE_OF=y
+	default m if SPI_HID_APPLE_OF=m
+	select HID
+	select CRC16

drivers/hid/spi-hid/Makefile

@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Makefile for SPI HID tarnsport drivers
+#
+
+obj-$(CONFIG_SPI_HID_APPLE_CORE)		+= spi-hid-apple.o
+
+spi-hid-apple-objs				=  spi-hid-apple-core.o
+
+obj-$(CONFIG_SPI_HID_APPLE_OF)			+= spi-hid-apple-of.o