drivers: wifi: Add ESP8266 and ESP32 wifi modem driver

This adds support for the Espressif ESP8266 and ESP32 devices to be used
as peripherals on a UART.

There are two main AT command versions that can be selected, 1.7 and
2.0. Since they behave a bit different it is important to select the
one that matches the used in the firmware on your device.

When downloading large amounts of data it is highly recommended to
enable CONFIG_ESP_PASSIVE_TCP and flow control on the UART so that
data is not lost due to UART speed or receive buffer size.

Currently unsupported:
- Changing UDP endpoint with a sendto()
- Bind to a specific local port
- Server socket operations, ie listen() and accept()

Official AT firmware for ESP8266 and ESP32 can be found at:
https://github.com/espressif/esp-at

Signed-off-by: Tobias Svehagen <[email protected]>

drivers/wifi/CMakeLists.txt

@@ -3,3 +3,4 @@
 add_subdirectory_ifdef(CONFIG_WIFI_WINC1500	winc1500)
 add_subdirectory_ifdef(CONFIG_WIFI_SIMPLELINK	simplelink)
 add_subdirectory_ifdef(CONFIG_WIFI_ESWIFI	eswifi)
+add_subdirectory_ifdef(CONFIG_WIFI_ESP		esp)

drivers/wifi/Kconfig

@@ -32,5 +32,6 @@ config WIFI_OFFLOAD
 source "drivers/wifi/winc1500/Kconfig.winc1500"
 source "drivers/wifi/simplelink/Kconfig.simplelink"
 source "drivers/wifi/eswifi/Kconfig.eswifi"
+source "drivers/wifi/esp/Kconfig.esp"
 
 endif # WIFI

drivers/wifi/esp/CMakeLists.txt

@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: Apache-2.0
+
+if(CONFIG_WIFI_ESP)
+  zephyr_include_directories(./)
+
+  zephyr_library_include_directories(
+    ${ZEPHYR_BASE}/drivers/modem
+  )
+
+  zephyr_sources(
+    esp.c
+    esp_socket.c
+    esp_offload.c
+  )
+endif()

drivers/wifi/esp/Kconfig.esp

@@ -0,0 +1,70 @@
+# Copyright (c) 2019 Tobias Svehagen
+# SPDX-License-Identifier: Apache-2.0
+
+menuconfig WIFI_ESP
+	bool "Espressif ESP8266 and ESP32 support"
+	select MODEM
+	select MODEM_CONTEXT
+	select MODEM_CMD_HANDLER
+	select MODEM_IFACE_UART
+	select NET_L2_WIFI_MGMT
+	select WIFI_OFFLOAD
+
+if WIFI_ESP
+
+config WIFI_ESP_NAME
+	string "Driver name"
+	default "esp-wifi-modem"
+
+config WIFI_ESP_RX_STACK_SIZE
+	int "Stack size for the Espressif esp wifi driver RX thread"
+	default 1024
+	help
+	  This stack is used by the Espressif ESP RX thread.
+
+config WIFI_ESP_RX_THREAD_PRIORITY
+	int "Priority of RX thread"
+	default 7
+	help
+	  Priority of thread used for processing RX data.
+
+config WIFI_ESP_WORKQ_STACK_SIZE
+	int "Stack size for the esp driver work queue"
+	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 WIFI_ESP_WORKQ_THREAD_PRIORITY
+	int "Priority of work queue thread"
+	default 7
+	help
+	  Priority of thread used for processing driver work queue items.
+
+config WIFI_ESP_PASSIVE_TCP
+	bool "Use passive TCP"
+	help
+	  This lets the ESP handle the TCP window so that data can flow
+	  at a rate that the driver can handle. Without this, data might get
+	  lost if the driver cannot empty the device buffer quickly enough.
+
+choice
+	prompt "AT version"
+	default WIFI_ESP_AT_VERSION_2_0
+	help
+	  Select which version of AT command set should be used.
+
+config  WIFI_ESP_AT_VERSION_1_7
+	bool "AT version 1.7"
+	help
+	  Use AT command set version 1.7.
+
+config WIFI_ESP_AT_VERSION_2_0
+	bool "AT version 2.0"
+	help
+	  Use AT command set version 2.0.
+
+endchoice
+
+endif # WIFI_ESP