On 09.04.21 02:39, Sven Van Asbroeck wrote:
> From: Sven Van Asbroeck <thesve...@gmail.com>
>
> The ethernet frame length is calculated incorrectly. Depending on
> the value of RX_HEAD_PADDING, this may result in ethernet frames
> that are too short (cut off at the end), or too long (garbage added
> to the end).
>
> Fix by calculating the ethernet frame length correctly. For added
> clarity, use the ETH_FCS_LEN constant in the calculation.
>
> Many thanks to Heiner Kallweit for suggesting this solution.
>
> Fixes: 3e21a10fdea3 ("lan743x: trim all 4 bytes of the FCS; not just 2")
> Link: https://lore.kernel.org/lkml/20210408172353.21143-1-thesve...@gmail.com/
> Signed-off-by: Sven Van Asbroeck <thesve...@gmail.com>
> ---
>
> Tree: git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git #
> 864db232dc70
>
> To: Bryan Whitehead <bryan.whiteh...@microchip.com>
> To: "David S. Miller" <da...@davemloft.net>
> To: Jakub Kicinski <k...@kernel.org>
> To: George McCollister <george.mccollis...@gmail.com>
> Cc: Heiner Kallweit <hkallwe...@gmail.com>
> Cc: Andrew Lunn <and...@lunn.ch>
> Cc: unglinuxdri...@microchip.com
> Cc: netdev@vger.kernel.org
> Cc: linux-ker...@vger.kernel.org
>
> drivers/net/ethernet/microchip/lan743x_main.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/ethernet/microchip/lan743x_main.c
> b/drivers/net/ethernet/microchip/lan743x_main.c
> index 1c3e204d727c..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;
>
On a cursory glance, using __netdev_alloc_skb_ip_align() here should
allow you to get rid of all the RX_HEAD_PADDING gymnastics.
And also avoid the need for setting RX_CFG_B_RX_PAD_2_, as the
NET_IP_ALIGN part would no longer get dma-mapped.
> 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 - 4);
> + 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;
>
