[PATCH net] net: stmmac: xgmac: do not treat TBU as a TX event

[Pengfei Zhang]

> [Severity: Medium]
> Can the XDP_TX and ndo_xdp_xmit path stall permanently on XGMAC in
> shared-IRQ mode when the TX coalesce timer is disabled?

This is not caused by this patch. It needs a very specific setup: XDP
TX traffic, tx-usecs set to 0, and tx-frames too large to be reached
below STMMAC_TX_THRESH. With that setup the same stall can already
happen on XGMAC with per-channel MSI today, because
stmmac_xdp_xmit_xdpf() only sets IC on a tx_coal_frames boundary and
has no fallback when the TX timer is disabled.

I will look at fixing that in the XDP TX path with a separate patch,
but it is independent of this one.

> [Severity: Medium]
> This isn't a bug introduced by this patch, but does
> dwmac4_dma_interrupt() in dwmac4_lib.c have the same sticky TBU
> problem?

Yes, it looks like it does, especially since commit 6ccf12ae111e
("net: stmmac: use interrupt mode INTM=1 for multi-MSI") moved the TBU
check out of the NIS block. I only have XGMAC hardware at the moment,
so I kept this patch to XGMAC. I will send a separate patch for dwmac4
once I can test it on dwmac4 hardware.