net: ks8851: Set initial carrier state to down [Linux 5.1]

net: ks8851: Set initial carrier state to down [Linux 5.1]

This Linux kernel change "net: ks8851: Set initial carrier state to down" is included in the Linux 5.1 release. This change is authored by Lukas Wunner <lukas [at] wunner.de> on Wed Mar 20 15:02:00 2019 +0100. The commit for this change in Linux stable tree is 9624baf (patch).

net: ks8851: Set initial carrier state to down

The ks8851 chip's initial carrier state is down. A Link Change Interrupt
is signaled once interrupts are enabled if the carrier is up.

The ks8851 driver has it backwards by assuming that the initial carrier
state is up. The state is therefore misrepresented if the interface is
opened with no cable attached. Fix it.

The Link Change interrupt is sometimes not signaled unless the P1MBSR
register (which contains the Link Status bit) is read on ->ndo_open().
This might be a hardware erratum. Read the register by calling
mii_check_link(), which has the desirable side effect of setting the
carrier state to down if the cable was detached while the interface was
closed.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Frank Pavlic <f.pavlic@kunbus.de>
Cc: Ben Dooks <ben.dooks@codethink.co.uk>
Cc: Tristram Ha <Tristram.Ha@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

There are 2 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/net/ethernet/micrel/ks8851.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/micrel/ks8851.c b/drivers/net/ethernet/micrel/ks8851.c
index c9faec4..b83b070 100644
--- a/drivers/net/ethernet/micrel/ks8851.c
+++ b/drivers/net/ethernet/micrel/ks8851.c
@@ -858,6 +858,7 @@ static int ks8851_net_open(struct net_device *dev)
    netif_dbg(ks, ifup, ks->netdev, "network device up\n");

    mutex_unlock(&ks->lock);
+   mii_check_link(&ks->mii);
    return 0;
 }

@@ -1519,6 +1520,7 @@ static int ks8851_probe(struct spi_device *spi)

    spi_set_drvdata(spi, ks);

+   netif_carrier_off(ks->netdev);
    ndev->if_port = IF_PORT_100BASET;
    ndev->netdev_ops = &ks8851_netdev_ops;
    ndev->irq = spi->irq;

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