HID: add spi-hid, transport driver for HID over SPI bus

This driver follows HID Over SPI Protocol Specification 1.0 available at
https://www.microsoft.com/en-us/download/details.aspx?id=103325. The
initial version of the driver does not support: 1) multi-fragment input
reports, 2) sending GET_INPUT and COMMAND output report types and
processing their respective acknowledge input reports, and 3) device
sleep power state.

Signed-off-by: Dmitry Antipov <dmanti@microsoft.com>

drivers/hid/Kconfig

@@ -1330,6 +1330,8 @@ source "drivers/hid/usbhid/Kconfig"
 
 source "drivers/hid/i2c-hid/Kconfig"
 
+source "drivers/hid/spi-hid/Kconfig"
+
 source "drivers/hid/intel-ish-hid/Kconfig"
 
 source "drivers/hid/amd-sfh-hid/Kconfig"

drivers/hid/Makefile

@@ -152,6 +152,7 @@ obj-$(CONFIG_USB_MOUSE)		+= usbhid/
 obj-$(CONFIG_USB_KBD)		+= usbhid/
 
 obj-$(CONFIG_I2C_HID_CORE)	+= i2c-hid/
+obj-$(CONFIG_SPI_HID)		+= spi-hid/
 
 obj-$(CONFIG_INTEL_ISH_HID)	+= intel-ish-hid/
 obj-$(INTEL_ISH_FIRMWARE_DOWNLOADER)	+= intel-ish-hid/

drivers/hid/spi-hid/Kconfig

@@ -0,0 +1,25 @@
+#
+# Copyright (c) 2021 Microsoft Corporation
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License version 2 as published by
+# the Free Software Foundation.
+#
+menu "SPI HID support"
+	depends on SPI
+
+config SPI_HID
+	tristate "HID over SPI transport layer"
+	default n
+	depends on SPI && INPUT && OF
+	select HID
+	help
+	  Say Y here if you use a keyboard, a touchpad, a touchscreen, or any
+	  other HID based devices which is connected to your computer via SPI.
+
+	  If unsure, say N.
+
+	  This support is also available as a module.  If so, the module
+	  will be called spi-hid.
+
+endmenu

drivers/hid/spi-hid/Makefile

@@ -0,0 +1,12 @@
+#
+# Copyright (c) 2021 Microsoft Corporation
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License version 2 as published by
+# the Free Software Foundation.
+#
+# Makefile for the HID over SPI transport driver
+#
+CFLAGS_trace.o = -I$(src)
+obj-$(CONFIG_SPI_HID)	+= spi-hid.o
+spi-hid-objs := spi-hid-core.o spi-hid-of.o trace.o