firmware: Add Turris Mox rWTM firmware driver

This adds a driver to communicate with the firmware running on the
secure processor of the Turris Mox router, enabling the kernel to
retrieve true random numbers from the Entropy Bit Generator and to read
some information burned into eFuses when device was manufactured:

and to
sign messages with the ECDSA private key burned into each Turris Mox
device when manufacturing.

This also adds support to read other information burned into eFuses:
 - serial number
 - board version
 - MAC addresses
 - RAM size
 - ECDSA public key (this is not read directly from eFuses, rather it
   is computed by the firmware as pair to the burned private key)

The source code of the firmware is open source and can be found at
https://gitlab.labs.nic.cz/turris/mox-boot-builder/tree/master/wtmi

The firmware is also able to, on demand, sign messages with the burned
ECDSA private key, but since Linux's akcipher API is not yet stable
(and therefore not exposed to userspace via netlink), this functionality
is not supported yet.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Marek Behún <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>

MAINTAINERS

@@ -1637,6 +1637,7 @@ F:	Documentation/devicetree/bindings/firmware/cznic,turris-mox-rwtm.txt
 F:	Documentation/devicetree/bindings/gpio/gpio-moxtet.txt
 F:	include/linux/moxtet.h
 F:	drivers/bus/moxtet.c
+F:	drivers/firmware/turris-mox-rwtm.c
 F:	drivers/gpio/gpio-moxtet.c
 
 ARM/EBSA110 MACHINE SUPPORT

drivers/firmware/Kconfig

@@ -270,6 +270,20 @@ config TRUSTED_FOUNDATIONS
 
 	  Choose N if you don't know what this is about.
 
+config TURRIS_MOX_RWTM
+	tristate "Turris Mox rWTM secure firmware driver"
+	depends on ARCH_MVEBU || COMPILE_TEST
+	depends on HAS_DMA && OF
+	depends on MAILBOX
+	select HW_RANDOM
+	select ARMADA_37XX_RWTM_MBOX
+	help
+	  This driver communicates with the firmware on the Cortex-M3 secure
+	  processor of the Turris Mox router. Enable if you are building for
+	  Turris Mox, and you will be able to read the device serial number and
+	  other manufacturing data and also utilize the Entropy Bit Generator
+	  for hardware random number generation.
+
 config HAVE_ARM_SMCCC
 	bool
 

drivers/firmware/Makefile

@@ -22,6 +22,7 @@ obj-$(CONFIG_QCOM_SCM_32)	+= qcom_scm-32.o
 CFLAGS_qcom_scm-32.o :=$(call as-instr,.arch armv7-a\n.arch_extension sec,-DREQUIRES_SEC=1) -march=armv7-a
 obj-$(CONFIG_TI_SCI_PROTOCOL)	+= ti_sci.o
 obj-$(CONFIG_TRUSTED_FOUNDATIONS) += trusted_foundations.o
+obj-$(CONFIG_TURRIS_MOX_RWTM)	+= turris-mox-rwtm.o
 
 obj-$(CONFIG_ARM_SCMI_PROTOCOL)	+= arm_scmi/
 obj-y				+= psci/