Re: [net-next PATCH 1/4] drivers: net: dsa: qca8k: drop MTU tracking from qca8k_priv

[Vladimir Oltean <olteanv@gmail.com>]

On Tue, Mar 22, 2022 at 02:45:03AM +0100, Ansuel Smith wrote:
> Drop the MTU array from qca8k_priv and use slave net dev to get the max
> MTU across all user port. CPU port can be skipped as DSA already make
> sure CPU port are set to the max MTU across all ports.
> 
> Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
> ---

I hardly find this to be an improvement and I would rather not see such
unjustified complexity in a device driver. What are the concrete
benefits, size wise?

>  drivers/net/dsa/qca8k.c | 38 +++++++++++++++++++++++---------------
>  drivers/net/dsa/qca8k.h |  1 -
>  2 files changed, 23 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/dsa/qca8k.c b/drivers/net/dsa/qca8k.c
> index d3ed0a7f8077..4366d87b4bbd 100644
> --- a/drivers/net/dsa/qca8k.c
> +++ b/drivers/net/dsa/qca8k.c
> @@ -2367,13 +2367,31 @@ static int
>  qca8k_port_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
>  {
>  	struct qca8k_priv *priv = ds->priv;
> -	int i, mtu = 0;
> +	struct dsa_port *dp;
> +	int mtu = new_mtu;
>  
> -	priv->port_mtu[port] = new_mtu;
> +	/* We have only have a general MTU setting. So check
> +	 * every port and set the max across all port.
> +	 */
> +	list_for_each_entry(dp, &ds->dst->ports, list) {
> +		/* We can ignore cpu port, DSA will itself chose
> +		 * the max MTU across all port
> +		 */
> +		if (!dsa_port_is_user(dp))
> +			continue;
>  
> -	for (i = 0; i < QCA8K_NUM_PORTS; i++)
> -		if (priv->port_mtu[i] > mtu)
> -			mtu = priv->port_mtu[i];
> +		if (dp->index == port)
> +			continue;
> +
> +		/* Address init phase where not every port have
> +		 * a slave device
> +		 */
> +		if (!dp->slave)
> +			continue;
> +
> +		if (mtu < dp->slave->mtu)
> +			mtu = dp->slave->mtu;
> +	}
>  
>  	/* Include L2 header / FCS length */
>  	return qca8k_write(priv, QCA8K_MAX_FRAME_SIZE, mtu + ETH_HLEN + ETH_FCS_LEN);
> @@ -3033,16 +3051,6 @@ qca8k_setup(struct dsa_switch *ds)
>  				  QCA8K_PORT_HOL_CTRL1_WRED_EN,
>  				  mask);
>  		}
> -
> -		/* Set initial MTU for every port.
> -		 * We have only have a general MTU setting. So track
> -		 * every port and set the max across all port.
> -		 * Set per port MTU to 1500 as the MTU change function
> -		 * will add the overhead and if its set to 1518 then it
> -		 * will apply the overhead again and we will end up with
> -		 * MTU of 1536 instead of 1518
> -		 */
> -		priv->port_mtu[i] = ETH_DATA_LEN;
>  	}
>  
>  	/* Special GLOBAL_FC_THRESH value are needed for ar8327 switch */
> diff --git a/drivers/net/dsa/qca8k.h b/drivers/net/dsa/qca8k.h
> index f375627174c8..562d75997e55 100644
> --- a/drivers/net/dsa/qca8k.h
> +++ b/drivers/net/dsa/qca8k.h
> @@ -398,7 +398,6 @@ struct qca8k_priv {
>  	struct device *dev;
>  	struct dsa_switch_ops ops;
>  	struct gpio_desc *reset_gpio;
> -	unsigned int port_mtu[QCA8K_NUM_PORTS];
>  	struct net_device *mgmt_master; /* Track if mdio/mib Ethernet is available */
>  	struct qca8k_mgmt_eth_data mgmt_eth_data;
>  	struct qca8k_mib_eth_data mib_eth_data;
> -- 
> 2.34.1
>