netdev - Re: [PATCH v3 1/3] dsa: marvell: Provide per device information about max frame size

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Date:   Mon, 2 Jan 2023 21:29:13 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Lukasz Majewski <lukma@...x.de>
Cc:     Vladimir Oltean <olteanv@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] dsa: marvell: Provide per device information
 about max frame size

> @@ -3548,7 +3548,9 @@ static int mv88e6xxx_get_max_mtu(struct dsa_switch *ds, int port)
>  	if (chip->info->ops->port_set_jumbo_size)
>  		return 10240 - VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN;
>  	else if (chip->info->ops->set_max_frame_size)
> -		return 1632 - VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN;
> +		return (max_t(int, chip->info->max_frame_size, 1632)
> +			- VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN);
> +
>  	return 1522 - VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN;

I would also prefer if all this if/else logic is removed, and the code
simply returned chip->info->max_frame_size - VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN;

> +++ b/drivers/net/dsa/mv88e6xxx/chip.h
> @@ -132,6 +132,7 @@ struct mv88e6xxx_info {
>  	unsigned int num_gpio;
>  	unsigned int max_vid;
>  	unsigned int max_sid;
> +	unsigned int max_frame_size;

It might be worth adding a comment here what this value actually
represents. We don't want any mixups where the value already has the
frame checksum removed for example.

      Andrew