netdev - Re: [PATCH net-next] net: dsa: mv88e6xxx: don't set non-existing learn2all bit for 6220/6250

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Message-ID: <20201208142519.GK2475764@lunn.ch>
Date:   Tue, 8 Dec 2020 15:25:19 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     netdev@...r.kernel.org, Vivien Didelot <vivien.didelot@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Vladimir Oltean <olteanv@...il.com>,
        Hubert Feurstein <h.feurstein@...il.com>
Subject: Re: [PATCH net-next] net: dsa: mv88e6xxx: don't set non-existing
 learn2all bit for 6220/6250

On Tue, Dec 08, 2020 at 10:01:09AM +0100, Rasmus Villemoes wrote:
> The 6220 and 6250 switches do not have a learn2all bit in global1, ATU
> control register; bit 3 is reserved.
> 
> On the switches that do have that bit, it is used to control whether
> learning frames are sent out the ports that have the message_port bit
> set. So rather than adding yet another chip method, use the existence
> of the ->port_setup_message_port method as a proxy for determining
> whether the learn2all bit exists (and should be set).
> 
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
> ---
> 
> This doesn't fix anything from what I can tell, in particular not the
> VLAN problems I'm having, so just tagging for net-next. But I do think
> it's worth it on the general principle of not poking around in
> undocumented/reserved bits.
> 
>  drivers/net/dsa/mv88e6xxx/chip.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
> index 25449f634889..0245f3dfc1cd 100644
> --- a/drivers/net/dsa/mv88e6xxx/chip.c
> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
> @@ -1347,9 +1347,11 @@ static int mv88e6xxx_atu_setup(struct mv88e6xxx_chip *chip)
>  	if (err)
>  		return err;
>  
> -	err = mv88e6xxx_g1_atu_set_learn2all(chip, true);
> -	if (err)
> -		return err;
> +	if (chip->info->ops->port_setup_message_port) {
> +		err = mv88e6xxx_g1_atu_set_learn2all(chip, true);
> +		if (err)
> +			return err;
> +	}

Hi Rasmus

This needs a comment in the code explaining why this odd structure is
used.

	Andrew