[PATCHv4 3/5] net/lwip: add doc/develop/net_lwip.rst

[Ilias Apalodimas]

Hi Maxim,

On Fri, Jul 14, 2023 at 08:19:58PM +0600, Maxim Uvarov wrote:
> Just add inital doc.
> 
> Signed-off-by: Maxim Uvarov <maxim.uvarov at 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..567234fff2
> --- /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

s/for implementation/implementing/

> +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

s/And it was more easy/it turned out easier to/

> +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

s/Raw IP IP means/In raw IP mode a callback function etc

> +data passes the IP stack and is ready for the application.

is passed to the ip stack?

> +
> +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.

I think you can drop this entirely and we can add it if we ever want to
support sockets

> +
> +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
> 

Thanks
/Ilias