Re: [lwip-devel] [PATCHv3 3/3] net/lwip: add doc/develop/net_lwip.rst

[Simon Glass]

Hi Maxim,

On Wed, 5 Jul 2023 at 09:17, Maxim Uvarov <maxim.uvarov@linaro.org> wrote:
>
> 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

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.
> --
> 2.30.2
>

Regards,
SImon