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

Contains "HID: transport: spi: apple: Increase receive buffer size"

The SPI receive buffer is passed directly to hid_input_report() if it
contains a complete report. It is then passed to hid_report_raw_event()
which computes the expected report size and memsets the "missing
trailing data up to HID_MAX_BUFFER_SIZE (16K) or
hid_ll_driver.max_buffer_size (if set) to zero.

Co-developed-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Janne Grunau <j@jannau.net>

Author: jannau

drivers/hid/Kconfig

@@ -1446,4 +1446,6 @@ endif # HID
 
 source "drivers/hid/usbhid/Kconfig"
 
+source "drivers/hid/spi-hid/Kconfig"
+
 endif # HID_SUPPORT

drivers/hid/Makefile

@@ -173,6 +173,8 @@ obj-$(CONFIG_INTEL_ISH_HID)	+= intel-ish-hid/
 
 obj-$(CONFIG_AMD_SFH_HID)       += amd-sfh-hid/
 
+obj-$(CONFIG_SPI_HID_APPLE_CORE)	+= spi-hid/
+
 obj-$(CONFIG_SURFACE_HID_CORE)  += surface-hid/
 
 obj-$(CONFIG_INTEL_THC_HID)     += intel-thc-hid/

drivers/hid/spi-hid/Kconfig

@@ -0,0 +1,24 @@
+# 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"
+	depends on INPUT && OF
+	select SPI_HID_APPLE_CORE
+	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
+	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