[PATCHv6 01/14] net/lwip: add doc/develop/net_lwip.rst

[Maxim Uvarov]

Add initial documentation of lwIP network IP stack integration
to the U-Boot (net_lwip.rst).

Signed-off-by: Maxim Uvarov <maxim.uvarov at linaro.org>
Reviewed-by: Simon Glass <sjg at chromium.org>
---
 doc/develop/index.rst    |  1 +
 doc/develop/net_lwip.rst | 64 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 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..bdd2c921b3
--- /dev/null
+++ b/doc/develop/net_lwip.rst
@@ -0,0 +1,64 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+LWIP IP stack intergation 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 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. 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.
+
+Example is 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. So we do not touch any drivers code and just eat
+packets when they are ready.
-- 
2.30.2