Subject: Re: [PATCH net 09/13] net: stmmac: Remove default maxmtu DT-platform setting

From: Piotr Raczynski <[email-masked]>
Date: Tue, 14 Mar 2023 12:20:18 +0100

On Tue, Mar 14, 2023 at 01:42:33AM +0300, Serge Semin wrote:
> Initializing maxmtu platform parameter in the stmmac_probe_config_dt()
> method by default makes being pointless the DW MAC-specific maximum MTU
> selection algorithm implemented in the stmmac_dvr_probe() method. At least
> for xGMAC we'll always have a frame MTU limited with 9000 while it
> supports units up to 16KB. Let's remove the default initialization of
> the maxmtu platform setting then. We don't replace it with setting the
> maxmtu with some greater value because a default maximum MTU is
> calculated later in the stmmac_dvr_probe() anyway. That would have been a
> pointless limitation too. Instead from now the main STMMAC driver code
> will consider the out of bounds maxmtu value as invalid and will silently
> replace it with a maximum MTU value specific to the corresponding DW MAC.
> 
> Note this alteration will only affect the xGMAC IP-cores due to the way
> the MTU autodetecion algorithm is implemented. So from now the driver will
> permit DW xGMACs to handle frames up to 16KB length (XGMAC_JUMBO_LEN). As
> before DW GMAC IP-cores of v4.0 and higher and IP-cores with enhanced
> descriptor support will be able to work with frames up to 8KB (JUMBO_LEN).
> The rest of the NICs will support frames of SKB_MAX_HEAD(NET_SKB_PAD +
> NET_IP_ALIGN) size.
> 
> Fixes: 7d9e6c5afab6 ("net: stmmac: Integrate XGMAC into main driver flow")
> Signed-off-by: Serge Semin <[email-masked]>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c     | 4 ----
>  drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c | 5 -----
>  2 files changed, 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 32aa7953d296..e5cb4edc4e23 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -7252,10 +7252,6 @@ int stmmac_dvr_probe(struct device *device,
>  	if ((priv->plat->maxmtu < ndev->max_mtu) &&
>  	    (priv->plat->maxmtu >= ndev->min_mtu))
>  		ndev->max_mtu = priv->plat->maxmtu;
> -	else if (priv->plat->maxmtu < ndev->min_mtu)
> -		dev_warn(priv->device,
> -			 "%s: warning: maxmtu having invalid value (%d)\n",
> -			 __func__, priv->plat->maxmtu);

Looks fine but by removing plat->maxmtu = JUMBO_LEN; you eliminate the
case of dev_warn here or you remove dev_warn since the driver will be
able to fix the mtu value?
>  
>  	if (flow_ctrl)
>  		priv->flow_ctrl = FLOW_AUTO;	/* RX/TX pause on */
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> index 067a40fe0a23..857411105a0a 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> @@ -468,11 +468,6 @@ stmmac_probe_config_dt(struct platform_device *pdev, u8 *mac)
>  	plat->en_tx_lpi_clockgating =
>  		of_property_read_bool(np, "snps,en-tx-lpi-clockgating");
>  
> -	/* Set the maxmtu to a default of JUMBO_LEN in case the
> -	 * parameter is not present in the device tree.
> -	 */
> -	plat->maxmtu = JUMBO_LEN;
> -
>  	/* Set default value for multicast hash bins */
>  	plat->multicast_filter_bins = HASH_TABLE_SIZE;
>  
> -- 
> 2.39.2
> 
>