Re: [PATCH v2] net: mvneta: add basic XDP_DROP support

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

Hi Domagoj,

> > Add initial mvneta XDP support for hardware buffer management enabled
> > devices only.
> 
> Hi Domagoj,
> 
> I would really appreciate if we could coordinate our work on the mvneta
> driver.  Ilias (Cc'ed) and I are also working on adding XDP support for
> this driver, although this is the software-buffer side of the driver we
> have functioning now.

Yes please, Jesper and i didn't have access to hardware with BM. Let's sync up 
and try to provide XDP for both.

> 
> You can directly follow our progress here: [1][2]
>  [1] https://github.com/xdp-project/xdp-project/blob/master/areas/arm64/board_espressobin04_bench_xdp.org
>  [2] https://github.com/apalos/bpf-next/commits/mvneta_04_page_pool_recycle_xdp
> 
> You XDP-setup function is actually more correct that ours[3], as you
> handle BPF per queue (which we were planning to fix before upstreaming).
> 
> That said, adding XDP_DROP is easy, but I want to see more of the XDP
> features/actions added, as those require a lot more work.  I always
> worry that a driver will stop at just XDP_DROP, so what are your plans
> for adding the harder features? 
> 
> Even-thought XDP_DROP looks easy in this patch, then you are actually
> doing some wrong, as XDP can also modify frames before doing XDP_PASS,
> and (1) you have non-standard-head room (MVNETA_MH_SIZE + NET_SKB_PAD),
> (2) and you don't handle if XDP changed the xdp.data header pointer,
> and (3) you backing memory either comes from page-fragments or kmalloc
> which also goes against the XDP memory requirements.
> [3] https://github.com/apalos/bpf-next/commit/4b567e74552d3cdf55

Our patches use the page_pool API for this (the mvneta SWBM part of the driver 
was already allocating pages for backing up descriptors)

Thanks!
/Ilias