Re: [PATCH net-next 1/1] net: dsa: fix fixed-link port registration

[Marek Behun <marek.behun@nic.cz>]

This should probably go into stable as well, after review.

Marek

On Sun, 11 Aug 2019 03:46:50 +0200
Marek Behún <marek.behun@nic.cz> wrote:

> Commit 88d6272acaaa ("net: phy: avoid unneeded MDIO reads in
> genphy_read_status") broke fixed link DSA port registration in
> dsa_port_fixed_link_register_of: the genphy_read_status does not do what
> it is supposed to and the following adjust_link is given wrong
> parameters.
> 
> This causes a regression on Turris Omnia, where the mvneta driver for
> the interface connected to the switch reports crc errors, for some
> reason.
> 
> I realize this fix is not ideal, something else could change in genphy
> functions which could cause DSA fixed-link port to break again.
> Hopefully DSA fixed-link port functionality will be converted to phylink
> API soon.
> 
> Signed-off-by: Marek Behún <marek.behun@nic.cz>
> Cc: Heiner Kallweit <hkallweit1@gmail.com>
> Cc: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
> Cc: Vivien Didelot <vivien.didelot@gmail.com>
> Cc: Andrew Lunn <andrew@lunn.ch>
> Cc: Florian Fainelli <f.fainelli@gmail.com>
> Cc: David S. Miller <davem@davemloft.net>
> ---
>  net/dsa/port.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/net/dsa/port.c b/net/dsa/port.c
> index 363eab6df51b..c424ebb373e1 100644
> --- a/net/dsa/port.c
> +++ b/net/dsa/port.c
> @@ -485,6 +485,17 @@ static int dsa_port_fixed_link_register_of(struct dsa_port *dp)
>  	phydev->interface = mode;
>  
>  	genphy_config_init(phydev);
> +
> +	/*
> +	 * Commit 88d6272acaaa caused genphy_read_status not to do it's work if
> +	 * autonegotiation is enabled and link status did not change. This is
> +	 * the case for fixed_phy. By setting phydev->link = 0 before the call
> +	 * to genphy_read_status we force it to read and fill in the parameters.
> +	 *
> +	 * Hopefully this dirty hack will be removed soon by converting DSA
> +	 * fixed link ports to phylink API.
> +	 */
> +	phydev->link = 0;
>  	genphy_read_status(phydev);
>  
>  	if (ds->ops->adjust_link)