When repeatedly changing the interface link speed using the command below:

ethtool -s eth0 speed 100 duplex full
ethtool -s eth0 speed 1000 duplex full

The following errors may sometimes be reported by the ARM SMMU driver:

[ 5395.035364] fec 5b040000.ethernet eth0: Link is Down
[ 5395.039255] arm-smmu 51400000.iommu: Unhandled context fault:
fsr=0x402, iova=0x00000000, fsynr=0x100001, cbfrsynra=0x852, cb=2
[ 5398.108460] fec 5b040000.ethernet eth0: Link is Up - 100Mbps/Full -
flow control off

It is identified that the FEC driver does not properly stop the TX queue
during the link speed transitions, and this results in the invalid virtual
I/O address translations from the SMMU and causes the context faults.

Fixes: dbc64a8e ("net: fec: move calls to quiesce/resume packet processing out of fec_restart()")
Signed-off-by: Shenwei Wang <shenwei.wang@nxp.com>
Link: https://lore.kernel.org/r/20240123165141.2008104-1-shenwei.wang@nxp.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>