netdev - 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 14:35:29 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Heiner Kallweit <hkallweit1@...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"

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;

        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;