linux-kernel - Re: [PATCH net v1] Revert "lan743x: trim all 4 bytes of the FCS; not just 2"

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Date:   Thu, 8 Apr 2021 21:06:53 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     George McCollister <george.mccollister@...il.com>,
        Bryan Whitehead <bryan.whitehead@...rochip.com>,
        David S Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        netdev <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net v1] Revert "lan743x: trim all 4 bytes of the FCS; not
 just 2"

On 08.04.2021 20:35, Sven Van Asbroeck wrote:
> Hi George,
> 
> On Thu, Apr 8, 2021 at 2:26 PM Sven Van Asbroeck <thesven73@...il.com> wrote:
>>
>> George, I will send a patch for you to try shortly. Except if you're
>> already ahead :)
> 
> Would this work for you? It does for me.
> 
> diff --git a/drivers/net/ethernet/microchip/lan743x_main.c
> b/drivers/net/ethernet/microchip/lan743x_main.c
> index dbdfabff3b00..7b6794aa8ea9 100644
> --- a/drivers/net/ethernet/microchip/lan743x_main.c
> +++ b/drivers/net/ethernet/microchip/lan743x_main.c
> @@ -885,8 +885,8 @@ static int lan743x_mac_set_mtu(struct
> lan743x_adapter *adapter, int new_mtu)
>         }
> 
>         mac_rx &= ~(MAC_RX_MAX_SIZE_MASK_);
> -       mac_rx |= (((new_mtu + ETH_HLEN + 4) << MAC_RX_MAX_SIZE_SHIFT_) &
> -                 MAC_RX_MAX_SIZE_MASK_);
> +       mac_rx |= (((new_mtu + ETH_HLEN + ETH_FCS_LEN)
> +                 << MAC_RX_MAX_SIZE_SHIFT_) & MAC_RX_MAX_SIZE_MASK_);
>         lan743x_csr_write(adapter, MAC_RX, mac_rx);
> 
>         if (enabled) {
> @@ -1944,7 +1944,7 @@ static int lan743x_rx_init_ring_element(struct
> lan743x_rx *rx, int index)
>         struct sk_buff *skb;
>         dma_addr_t dma_ptr;
> 
> -       buffer_length = netdev->mtu + ETH_HLEN + 4 + RX_HEAD_PADDING;
> +       buffer_length = netdev->mtu + ETH_HLEN + ETH_FCS_LEN + RX_HEAD_PADDING;
> 

A completely unrelated question:
How about VLAN packets with a 802.1Q tag? Should VLAN_ETH_HLEN be used?


>         descriptor = &rx->ring_cpu_ptr[index];
>         buffer_info = &rx->buffer_info[index];
> @@ -2040,7 +2040,7 @@ lan743x_rx_trim_skb(struct sk_buff *skb, int frame_length)
>                 dev_kfree_skb_irq(skb);
>                 return NULL;
>         }
> -       frame_length = max_t(int, 0, frame_length - RX_HEAD_PADDING - 2);
> +       frame_length = max_t(int, 0, frame_length - ETH_FCS_LEN);
>         if (skb->len > frame_length) {
>                 skb->tail -= skb->len - frame_length;
>                 skb->len = frame_length;
>