Add initial documentation of lwIP network IP stack integration to the U-Boot (net_lwip.rst).
Signed-off-by: Maxim Uvarov maxim.uvarov@linaro.org Reviewed-by: Simon Glass sjg@chromium.org Reviewed-by: Ilias Apalodimas ilias.apalodimas@linaro.org Signed-off-by: Maxim Uvarov maxim.uvarov@linaro.org --- doc/develop/index.rst | 1 + doc/develop/net_lwip.rst | 75 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 76 insertions(+) create mode 100644 doc/develop/net_lwip.rst
diff --git a/doc/develop/index.rst b/doc/develop/index.rst index f82e148b10..14951712e4 100644 --- a/doc/develop/index.rst +++ b/doc/develop/index.rst @@ -50,6 +50,7 @@ Implementation spl falcon uefi/index + net_lwip vbe version
diff --git a/doc/develop/net_lwip.rst b/doc/develop/net_lwip.rst new file mode 100644 index 0000000000..a77ab60d0f --- /dev/null +++ b/doc/develop/net_lwip.rst @@ -0,0 +1,75 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +lwIP IP stack integration for U-Boot +==================================== + +Intro +----- + +lwIP is a library implementing network protocols, which is commonly used +on embedded devices. + +https://savannah.nongnu.org/projects/lwip/ +lwIP license: +lwIP is licensed under a BSD-style license: http://lwip.wikia.com/wiki/License. + +Main features include: + +* Protocols: IP, IPv6, ICMP, ND, MLD, UDP, TCP, IGMP, ARP, PPPoS, PPPoE + +* DHCP client, DNS client (incl. mDNS hostname resolver), + AutoIP/APIPA (Zeroconf), SNMP agent (v1, v2c, v3, private MIB support + & MIB compiler) + +* APIs: specialized APIs for enhanced performance, optional Berkeley-alike + socket API + +* Extended features: IP forwarding over multiple network interfaces, TCP + congestion control, RTT estimation and fast recovery/fast retransmit + +* Addon applications: HTTP(S) server, SNTP client, SMTP(S) client, ping, + NetBIOS nameserver, mDNS responder, MQTT client, TFTP server + +U-Boot implementation details +----------------------------- + +1. In general we can build lwIP as a library and link it against U-Boot or + compile it in the U-Boot tree in the same way as other U-Boot files. There + are few reasons why second variant was selected: lwIP is very customizable + with defines for features, memory size, types of allocation, some internal + types and platform specific code. It turned out easier to enable/disable + debug which is also done with defines, and is needed periodically. + +2. lwIP has 2 APIs - raw mode and sequential (as lwIP names it, or socket API + as we name it in Linux). For now only raw API is supported. + +In raw IP mode a callback function for RX path is registered and will be called +when packet is passed to the IP stack and is ready for the application. + +One example is the unmodified working ping example from lwip sources which +registered the callback: + +.. code-block:: c + + ping_pcb = raw_new(IP_PROTO_ICMP); + raw_recv(ping_pcb, ping_recv, NULL); <- ping_recv is app callback. + raw_bind(ping_pcb, IP_ADDR_ANY) + +3. Input and output + +RX packet path is injected to U-Boot eth_rx() polling loop and TX patch is in +eth_send() accordingly. That way we can leave the driver code unmodified and +consume packets once they are ready. So we do not touch any drivers code and +just eat packets when they are ready. + +U-Boot lwIP Applications +======================== + +.. kernel-doc:: include/net/lwip.h + :internal: + +lwIP API to control polling loop +================================ + +.. kernel-doc:: include/net/ulwip.h + :internal: