phy: make some bits preserved while setup forced mode

When tested the PHY SGMII Loopback:
1.set the LOOPBACK bit,
2.set the autoneg to AUTONEG_DISABLE, it calls the
genphy_setup_forced which will clear the bit.

The BMCR_LOOPBACK bit should be preserved.

As Florian pointed out that other bits should be preserved too.
So I make the BMCR_ISOLATE and BMCR_PDOWN as well.

Signed-off-by: Weidong Wang <wangweidong1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index e551f3a89cfd..10e39c2fbf81 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1123,8 +1123,9 @@ static int genphy_config_advert(struct phy_device *phydev)
  */
 int genphy_setup_forced(struct phy_device *phydev)
 {
-        int ctl = 0;
+        int ctl = phy_read(phydev, MII_BMCR);
 
+        ctl &= BMCR_LOOPBACK | BMCR_ISOLATE | BMCR_PDOWN;
         phydev->pause = 0;
         phydev->asym_pause = 0;