netdev - Re: [PATCH net-next 1/2] net: dsa: mv88e6xxx: fix RGMII-ID port setup

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Date:   Sun, 11 Aug 2019 17:31:53 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Marek Behún <marek.behun@....cz>
Cc:     netdev@...r.kernel.org, Heiner Kallweit <hkallweit1@...il.com>,
        Sebastian Reichel <sebastian.reichel@...labora.co.uk>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 1/2] net: dsa: mv88e6xxx: fix RGMII-ID port setup

On Sun, Aug 11, 2019 at 05:08:11PM +0200, Marek Behún wrote:
> The mv88e6xxx_port_setup_mac looks if one of the {link, speed, duplex}
> parameters is being changed from the current setting, and if not, does
> not do anything. This test is wrong in some situations: this method also
> has the mode argument, which can also be changed.
> 
> For example on Turris Omnia, the mode is PHY_INTERFACE_MODE_RGMII_ID,
> which has to be set byt the ->port_set_rgmii_delay method. The test does
> not look if mode is being changed (in fact there is currently no method
> to determine port mode as phy_interface_t type).
> 
> The simplest solution seems to be to drop this test altogether and
> simply do the setup when requested.

Hi Marek

Unfortunately, that code is there for a reason. phylink can call the
->mac_config() method once per second. It is documented that
mac_config() should only reconfigure what, if anything, has changed.
And mv88e6xxx_port_setup_mac() needs to disable the port in order to
change anything. So the change you propose here, under some
conditions, will cause the port to be disabled/enables once per
second.

We need to fix this by expanding the test, not removing it.  My
current _guess_ would be, we need to add a ops->port_get_rgmii_delay()
so we can see if that is what needs configuring.

   Andrew