XDP on agilex3

Hi Torstein18,

Stmmac does not implement a full zero‑copy TX path, even on recent kernels. The “few packets then stops” behavior you see is a classic symptom of that gap.

mas-bandwidth/af_xdp/001 is a pure AF_XDP userspace TX loop.

On stmmac, what typically happens:

1. First packets go out (driver does a fallback copy or partial DMA)
2. TX completion path never frees UMEM frames correctly
3. TX ring fills up
4. Kernel stops accepting new descriptors
5. sendto() succeeds briefly, then silently stalls

This is not a userspace bug in your example.

For AF_XDP ZC TX, the driver must implement:

ndo_xsk_wakeup

ZC‑capable TX rings

Correct UMEM lifetime handling

What does work reliably is XDP_TX / XDP_REDIRECT from an XDP program, not AF_XDP userspace TX ZC.

You may consider implementing below flow.

FPGA → shared memory → XDP program → XDP_TX

Key points:

• FPGA writes packet buffers into shared memory (ensure cache coherency/IO-MMU mapping is correct).
• CPU does NOT copy payload
• XDP program simply sets headers and returns XDP_TX
• No AF_XDP socket involved

Hope this is helpful.

Archer_Altera