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

[Ilias Apalodimas]

On Mon, Aug 14, 2023 at 07:32:40PM +0600, Maxim Uvarov wrote:
> 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

You can skip the 'I' here, it's not a personal project.  Something along
the lines of 'the second variant was chosen ...' would work 
> +   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

One example is the unmodified etc 

> +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.

'That way we can leave the driver code unmodified and consume packets once
they are ready'

Thanks
/Ilias
> -- 
> 2.30.2
>