Patch "net: dsa: actually force the speed on the CPU port" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

net: dsa: actually force the speed on the CPU port

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-dsa-actually-force-the-speed-on-the-cpu-port.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Russell King <[email protected]>
Date: Mon, 21 Sep 2015 21:42:59 +0100
Subject: net: dsa: actually force the speed on the CPU port

From: Russell King <[email protected]>

[ Upstream commit 53adc9e83028d9e35b6408231ebaf62a94a16e4d ]

Commit 54d792f257c6 ("net: dsa: Centralise global and port setup code into mv88e6xxx.") merged in the 4.2 merge window broke the link speed forcing for the CPU port of Marvell DSA switches. The original code was:

        /* MAC Forcing register: don't force link, speed, duplex
         * or flow control state to any particular values on physical
         * ports, but force the CPU port and all DSA ports to 1000 Mb/s
         * full duplex.
         */
        if (dsa_is_cpu_port(ds, p) || ds->dsa_port_mask & (1 << p))
                REG_WRITE(addr, 0x01, 0x003e);
        else
                REG_WRITE(addr, 0x01, 0x0003);

but the new code does a read-modify-write:

                reg = _mv88e6xxx_reg_read(ds, REG_PORT(port), PORT_PCS_CTRL);
                if (dsa_is_cpu_port(ds, port) ||
                    ds->dsa_port_mask & (1 << port)) {
                        reg |= PORT_PCS_CTRL_FORCE_LINK |
                                PORT_PCS_CTRL_LINK_UP |
                                PORT_PCS_CTRL_DUPLEX_FULL |
                                PORT_PCS_CTRL_FORCE_DUPLEX;
                        if (mv88e6xxx_6065_family(ds))
                                reg |= PORT_PCS_CTRL_100;
                        else
                                reg |= PORT_PCS_CTRL_1000;

The link speed in the PCS control register is a two bit field. Forcing the link speed in this way doesn't ensure that the bit field is set to the correct value - on the hardware I have here, the speed bitfield remains set to 0x03, resulting in the speed not being forced to gigabit.

We must clear both bits before forcing the link speed.

---
 drivers/net/dsa/mv88e6xxx.c |    1 +
 1 file changed, 1 insertion(+)

@@ -1387,6 +1387,7 @@ static int mv88e6xxx_setup_port(struct d
 		reg = _mv88e6xxx_reg_read(ds, REG_PORT(port), PORT_PCS_CTRL);
 		if (dsa_is_cpu_port(ds, port) ||
 		    ds->dsa_port_mask & (1 << port)) {
+			reg &= ~PORT_PCS_CTRL_UNFORCED;
 			reg |= PORT_PCS_CTRL_FORCE_LINK |
 				PORT_PCS_CTRL_LINK_UP |
 				PORT_PCS_CTRL_DUPLEX_FULL |

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/net-fec-clear-receive-interrupts-before-processing-a-packet.patch queue-4.2/net-dsa-actually-force-the-speed-on-the-cpu-port.patch