Re: [PATCH] net: dsa: mv88e6xxx: prevent 2500BASEX mode override

From: Marek Behun <marek.behun@nic.cz>
To: Nathan Rossi <nathan@nathanrossi.com>
Cc: netdev@vger.kernel.org, Nathan Rossi <nathan.rossi@digi.com>,
	Andrew Lunn <andrew@lunn.ch>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Vladimir Oltean <olteanv@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Russell King <linux@armlinux.org.uk>
Subject: Re: [PATCH] net: dsa: mv88e6xxx: prevent 2500BASEX mode override
Date: Mon, 15 Feb 2021 14:47:56 +0100	[thread overview]
Message-ID: <20210215144756.76846c9b@nic.cz> (raw)
In-Reply-To: <20210215061559.1187396-1-nathan@nathanrossi.com>

On Mon, 15 Feb 2021 06:15:59 +0000
Nathan Rossi <nathan@nathanrossi.com> wrote:

> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
> index 54aa942eed..5c52906b29 100644
> --- a/drivers/net/dsa/mv88e6xxx/chip.c
> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
> @@ -650,6 +650,13 @@ static void mv88e6xxx_validate(struct dsa_switch *ds, int port,
>  	if (chip->info->ops->phylink_validate)
>  		chip->info->ops->phylink_validate(chip, port, mask, state);
>  
> +	/* Advertise 2500BASEX only if 1000BASEX is not configured, this
> +	 * prevents phylink_helper_basex_speed from always overriding the
> +	 * 1000BASEX mode since auto negotiation is always enabled.
> +	 */
> +	if (state->interface == PHY_INTERFACE_MODE_1000BASEX)
> +		phylink_clear(mask, 2500baseX_Full);
> +

I don't quite like this. This problem should be either solved in
phylink_helper_basex_speed() or somewhere in the mv88e6xxx code, but near
the call to phylink_helper_basex_speed().

Putting a solution to the behaviour of phylink_helper_basex_speed() it
into the validate() method when phylink_helper_basex_speed() is called
from a different place will complicate debugging in the future. If
we start solving problems in this kind of way, the driver will become
totally unreadable, IMO.

Marek