[PATCHv10 03/15] net/lwip: add doc/develop/net_lwip.rst

Maxim Uvarov
2023-09-26T09:44:13Z

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>
---
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 5b230d0321..4764990f25 100644
--- a/doc/develop/index.rst
+++ b/doc/develop/index.rst
@@ -48,6 +48,7 @@ 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:
--
2.30.2