Just add inital doc.
Signed-off-by: Maxim Uvarov maxim.uvarov@linaro.org --- doc/develop/index.rst | 1 + doc/develop/net_lwip.rst | 59 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 60 insertions(+) create mode 100644 doc/develop/net_lwip.rst
diff --git a/doc/develop/index.rst b/doc/develop/index.rst index 97c526e997..a092c33df0 100644 --- a/doc/develop/index.rst +++ b/doc/develop/index.rst @@ -43,6 +43,7 @@ Implementation smbios spl 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..2520fe11b1 --- /dev/null +++ b/doc/develop/net_lwip.rst @@ -0,0 +1,59 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +LWIP IP stack intergation for U-boot +==================================== + +Intro +----- + +LWIP is a library for implementation 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 I selected +the second variant: LwIP is very customizable with defines for features, memory size, types of +allocation, some internal types and platform specific code. And it was more easy 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. + +Raw IP means that the call back function for RX path is registered and will be called when packet +data passes the IP stack and is ready for the application. + +Example is unmodified working ping example from lwip sources which registeres 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) + +Socket API also gives nice advantages due it will be easy to port linux socket applications to u-boot. +I.e. LwIP sockets compatible with the linux ones. But that will require RX thread running in the background. +So that means we need some kind of scheduler, locking and threading support or find some other solution. + +3. Input and output + +RX packet path is injected to U-boot eth_rx() polling loop and TX patch is in eth_send() accordingly. +So we do not touch any drivers code and just eat packets when they are ready.