net: enetc: restore RX ring congestion mode after ring reconfiguration

The RX ring congestion mode (CM) is only configured in the phylink
.mac_link_up() callback enetc_pl_mac_link_up(), which sets the
ENETC_RBMR_CM bit when tx_pause is enabled. This callback runs only when
the link status changes.

However, enetc_reconfigure() tears down and re-creates the RX BD rings at
runtime without any link status change, for example when attaching or
detaching an XDP program, or when enabling/disabling PTP RX hardware
timestamping. The rings are rebuilt from a cleared RBMR, so the CM bit is
lost. Since the link status does not change, enetc_pl_mac_link_up() is
not called again and the CM bit is never restored.

As a result, the ENETC MAC can no longer generate PAUSE frames on ingress
congestion, and flow control stops working after such a reconfiguration.

Track the desired CM state in a software flag ENETC_RXBDR_CM. Set or clear
this flag in enetc_pl_mac_link_up() according to tx_pause. When the RX BD
rings are (re)enabled, enetc_enable_rxbdr() consults this flag and restores
the ENETC_RBMR_CM bit accordingly, so flow control survives ring
reconfiguration even when the link status does not change.

RBMR is now written as a whole word from enetc_enable_rxbdr() rather than
by read-modify-write from several call sites. Serialize the remaining RBMR
read-modify-write paths, the congestion mode update and the RX VLAN offload
update, with the new si->gen_lock so they cannot race each other.

Fixes: 5093406c784f ("net: enetc: implement ring reconfiguration procedure for PTP RX timestamping")
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260821064140.1315611-2-wei.fang@oss.nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions