[PATCH net-next 0/2] net: fec: support RX flushing via fsl,rx-flush-queues

From: Alexander Sverdlin <alexander.sverdlin@siemens.com>

The FEC/ENET controller can flush frames that get stuck at the head of the
RX FIFO because their destination ring has no empty buffer descriptor
(RxBD[E] clear or ENET_RDARn not set). Without flushing, such a frame blocks
the FIFO and stalls reception on all queues; with flushing enabled the
offending frame is discarded instead. Flushing is configured per RX queue
through the RX_FLUSHn bits of the QOS Scheme register (FEC_QOS_SCHEME).

This series adds a device tree property, fsl,rx-flush-queues, listing the RX
queues for which flushing should be enabled, and programs the corresponding
RX_FLUSHn bits.

Erratum ERR050395 (e.g. i.MX8QXP) can lock up the RX path when flushing is
enabled on more than one queue at the same time; recovery requires a full
ENET reset. Rather than encoding that hardware limitation in the binding,
the DT property is kept generic and the single-queue restriction is enforced
in the driver: a configuration enabling flushing on multiple queues is
rejected unless the controller advertises FEC_QUIRK_HAS_MULTI_RX_FLUSH.
Future parts with the erratum fixed can set that quirk to allow flushing on
several queues.

Example:

    &fec {
        fsl,num-rx-queues = <3>;
        fsl,rx-flush-queues = <1>;
    };

Alexander Sverdlin (2):
  dt-bindings: net: fsl,fec: add fsl,rx-flush-queues
  net: fec: support receive flushing via fsl,rx-flush-queues

 .../devicetree/bindings/net/fsl,fec.yaml      | 14 ++++++++
 drivers/net/ethernet/freescale/fec.h          | 14 ++++++++
 drivers/net/ethernet/freescale/fec_main.c     | 34 +++++++++++++++++++
 3 files changed, 63 insertions(+)

-- 
2.55.0