drivers: modem: add Wistron WNC-M14A2A LTE-M Modem Driver

The WNC-M14A2A (LTE / LTE-M) modem is presented as an Arduino-
compatible shield via AT&T's IoT Starter Kit v1.0.  It was
originally intended to work with the FRDM-K64F board, but
in theory as long as the right pins are configured it can
work with any board that supports Arduino-compatible headers.

The driver utilizes the CONFIG_NET_OFFLOAD setting to avoid the
normal handling of IP packets, and instead uses a socket-like
UART interface to handle incoming and outgoing data.

Signed-off-by: Michael Scott <mike@foundries.io>

drivers/modem/CMakeLists.txt

@@ -1 +1,2 @@
 zephyr_sources_ifdef(CONFIG_MODEM_RECEIVER modem_receiver.c)
+zephyr_sources_ifdef(CONFIG_MODEM_WNCM14A2A wncm14a2a.c)

drivers/modem/Kconfig

@@ -32,6 +32,50 @@ config MODEM_RECEIVER_MAX_CONTEXTS
 	  Maximum number of modem receiver contexts to handle.  For most
 	  purposes this should stay at 1.
 
+config MODEM_WNCM14A2A
+	bool "Enable Wistron LTE-M modem driver"
+	depends on UART_INTERRUPT_DRIVEN
+	select MODEM_RECEIVER
+	select NET_OFFLOAD
+	help
+	  Choose this setting to enable Wistron WNC-M14A2A LTE-M modem driver.
+	  NOTE: Currently the pin settings only work with FRDM K64F shield.
+
+config MODEM_WNCM14A2A_RX_STACK_SIZE
+	int "Size of the stack for the WNC-M14A2A modem driver RX thread"
+	depends on MODEM_WNCM14A2A
+	default 1028
+	help
+	  This stack is used by the WNCM14A2A RX thread.
+
+config MODEM_WNCM14A2A_RX_WORKQ_STACK_SIZE
+	int "Size of the stack for the WNC-M14A2A modem driver work queue"
+	depends on MODEM_WNCM14A2A
+	default 2048
+	help
+	  This stack is used by the work queue to pass off net_pkt data
+	  to the rest of the network stack, letting the rx thread continue
+	  processing data.
+
+config MODEM_WNCM14A2A_APN_NAME
+	string "APN name for establishing network connection"
+	depends on MODEM_WNCM14A2A
+	default "m2m.com.attz"
+	help
+	  This setting is used in the AT%PDNSET command to set the APN name
+	  for the network connection context.  Normally, don't need to change
+	  this value.
+
+config MODEM_WNCM14A2A_INIT_PRIORITY
+	int "WNC-M14A2A driver init priority"
+	depends on MODEM_WNCM14A2A
+	default 80
+	help
+	  WNC-M14A2A device driver initialization priority.
+	  Do not mess with it unless you know what you are doing.
+	  Note that the priority needs to be lower than the net stack
+	  so that it can start before the networking sub-system.
+
 config SYS_LOG_MODEM_LEVEL
 	int "Modem driver log level"
 	depends on SYS_LOG

dts/bindings/modem/wnc,m14a2a.yaml

@@ -0,0 +1,55 @@
+#
+# Copyright (c) 2018, Foundries.io
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+---
+title: WNC-M14A2A LTE-M Modem
+id: wnc,m14a2a
+version: 0.1
+
+description: >
+    This is a representation of the WNC-M14A2A LTE-M modem.
+
+inherits:
+    !include uart-device.yaml
+
+properties:
+    compatible:
+      type: string
+      category: required
+      constraint: "wnc,m14a2a"
+
+    mdm-boot-mode-sel-gpios:
+      type: compound
+      category: required
+      generation: define, use-prop-name
+
+    mdm-power-gpios:
+      type: compound
+      category: required
+      generation: define, use-prop-name
+
+    mdm-keep-awake-gpios:
+      type: compound
+      category: required
+      generation: define, use-prop-name
+
+    mdm-reset-gpios:
+      type: compound
+      category: required
+      generation: define, use-prop-name
+
+    mdm-shld-trans-ena-gpios:
+      type: compound
+      category: required
+      generation: define, use-prop-name
+
+    mdm-send-ok-gpios:
+      type: compound
+      category: optional
+      description: UART RTS pin if no HW flow control (set to always enabled)
+      generation: define, use-prop-name
+
+base_label: WNCM14A2A
+...