RE: [PATCH net-next] net: fec: support RX flushing via an ethtool private flag

[Wei Fang]

> The FEC controller can flush the RX FIFO of an individual receive queue
> through the RX_FLUSHn bits of the FEC_QOS_SCHEME (ENET_QOS) register.
> 
> RX flushing prevents frames in the RX FIFO from being blocked. Blocking
> can occur when the frame at the head of the RX FIFO cannot be forwarded
> because the ring it is associated with cannot accept it, i.e. when the
> ring's RxBD[EMPTY] is not set or ENET_RDARn is not set. When RX flushing
> is enabled for a ring, such a blocking frame is flushed (discarded)
> instead of stalling the FIFO and holding up the other rings.
> 
> Expose this per-queue capability as a runtime ethtool private flag
> ("rx-flush-qN").
> 
> Due to erratum ERR050395 (observed e.g. on i.MX8QXP), enabling RX flushing
> on more than one queue at a time can lock up the receive path, so only a
> single queue may have flushing enabled.
> 
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>

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