net: enetc: fix the incorrect clearing of IF_MODE bits

stable inclusion
from stable-5.10.71
commit b22c5e2c8e0380430a1c6d9ccbac8cb19d4ce986
bugzilla: 182981 https://gitee.com/openeuler/kernel/issues/I4I3KD

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b22c5e2c8e0380430a1c6d9ccbac8cb19d4ce986



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[ Upstream commit 325fd36a ]

The enetc phylink .mac_config handler intends to clear the IFMODE field
(bits 1:0) of the PM0_IF_MODE register, but incorrectly clears all the
other fields instead.

For normal operation, the bug was inconsequential, due to the fact that
we write the PM0_IF_MODE register in two stages, first in
phylink .mac_config (which incorrectly cleared out a bunch of stuff),
then we update the speed and duplex to the correct values in
phylink .mac_link_up.

Judging by the code (not tested), it looks like maybe loopback mode was
broken, since this is one of the settings in PM0_IF_MODE which is
incorrectly cleared.

Fixes: c76a9721 ("net: enetc: force the RGMII speed and duplex instead of operating in inband mode")
Reported-by: Pavel Machek (CIP) <pavel@denx.de>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>

Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>