netdev - Re: [PATCH net-next] mvpp2: document HW checksum behaviour

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Date:   Fri, 26 Jul 2019 14:57:15 +0200
From:   Antoine Tenart <antoine.tenart@...tlin.com>
To:     Matteo Croce <mcroce@...hat.com>
Cc:     netdev@...r.kernel.org,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Stefan Chulski <stefanc@...vell.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] mvpp2: document HW checksum behaviour

Hi Matteo,

On Fri, Jul 26, 2019 at 01:15:46AM +0200, Matteo Croce wrote:
> The hardware can only offload checksum calculation on first port due to
> the Tx FIFO size limitation. Document this in a comment.
> 
> Fixes: 576193f2d579 ("net: mvpp2: jumbo frames support")
> Signed-off-by: Matteo Croce <mcroce@...hat.com>

Looks good. Please note there's a similar code path in the probe. You
could also add a comment there (or move this check/comment in a common
place).

Thanks!
Antoine

> ---
>  drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> index d8e5241097a9..2f7286bd203b 100644
> --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> @@ -843,7 +843,10 @@ static int mvpp2_bm_update_mtu(struct net_device *dev, int mtu)
>  		/* Add port to new short & long pool */
>  		mvpp2_swf_bm_pool_init(port);
>  
> -		/* Update L4 checksum when jumbo enable/disable on port */
> +		/* Update L4 checksum when jumbo enable/disable on port.
> +		 * Only port 0 supports hardware checksum offload due to
> +		 * the Tx FIFO size limitation.
> +		 */
>  		if (new_long_pool == MVPP2_BM_JUMBO && port->id != 0) {
>  			dev->features &= ~(NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM);
>  			dev->hw_features &= ~(NETIF_F_IP_CSUM |
> -- 
> 2.21.0
> 

-- 
Antoine Ténart, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com