Re: [PATCH net-next v8 3/5] net: dsa: add out-of-band tagging protocol

[Jakub Kicinski <kuba@kernel.org>]

On Fri,  4 Nov 2022 18:41:49 +0100 Maxime Chevallier wrote:
> This tagging protocol is designed for the situation where the link
> between the MAC and the Switch is designed such that the Destination
> Port, which is usually embedded in some part of the Ethernet Header, is
> sent out-of-band, and isn't present at all in the Ethernet frame.
> 
> This can happen when the MAC and Switch are tightly integrated on an
> SoC, as is the case with the Qualcomm IPQ4019 for example, where the DSA
> tag is inserted directly into the DMA descriptors. In that case,
> the MAC driver is responsible for sending the tag to the switch using
> the out-of-band medium. To do so, the MAC driver needs to have the
> information of the destination port for that skb.
> 
> Add a new tagging protocol based on SKB extensions to convey the
> information about the destination port to the MAC driver

This is what METADATA_HW_PORT_MUX is for, you shouldn't have 
to allocate a piece of memory for every single packet.

Also the series doesn't build.