Re: [PATCH net-next 2/2] net: dsa: mv88e6xxx: Set link down when changing speed

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

On Mon, Mar 23, 2020 at 10:49:00PM +0100, Andrew Lunn wrote:
> The MAC control register must not be changed unless the link is down.
> Add the necassary call into mv88e6xxx_mac_link_up. Without it, the MAC
> does not change state, the link remains at the wrong speed.
> 
> Fixes: 30c4a5b0aad8 ("net: mv88e6xxx: use resolved link config in mac_link_up()")
> Signed-off-by: Andrew Lunn <andrew@lunn.ch>
> ---
>  drivers/net/dsa/mv88e6xxx/chip.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
> index dd8a5666a584..24ce17503950 100644
> --- a/drivers/net/dsa/mv88e6xxx/chip.c
> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
> @@ -733,6 +733,14 @@ static void mv88e6xxx_mac_link_up(struct dsa_switch *ds, int port,
>  
>  	mv88e6xxx_reg_lock(chip);
>  	if (!mv88e6xxx_port_ppu_updates(chip, port) || mode == MLO_AN_FIXED) {
> +		/* Port's MAC control must not be changed unless the
> +		 * link is down
> +		 */
> +		err = chip->info->ops->port_set_link(chip, port,
> +						     LINK_FORCED_DOWN);
> +		if (err)
> +			goto error;
> +

The port should be down at this point, otherwise the link state is not
matching phylink's idea of the state.  Your patch merely works around
that.  I think it needs solving properly.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 10.2Mbps down 587kbps up