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   1 From: Vladimir Oltean <vladimir.oltean@nxp.com>
   2 Date: Tue, 7 Feb 2023 12:30:27 +0200
   3 Subject: [PATCH] net: ethernet: mtk_eth_soc: fix DSA TX tag hwaccel for switch
   4  port 0
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   8
   9 Arınç reports that on his MT7621AT Unielec U7621-06 board and MT7623NI
  10 Bananapi BPI-R2, packets received by the CPU over mt7530 switch port 0
  11 (of which this driver acts as the DSA master) are not processed
  12 correctly by software. More precisely, they arrive without a DSA tag
  13 (in packet or in the hwaccel area - skb_metadata_dst()), so DSA cannot
  14 demux them towards the switch's interface for port 0. Traffic from other
  15 ports receives a skb_metadata_dst() with the correct port and is demuxed
  16 properly.
  17
  18 Looking at mtk_poll_rx(), it becomes apparent that this driver uses the
  19 skb vlan hwaccel area:
  20
  21         union {
  22                 u32             vlan_all;
  23                 struct {
  24                         __be16  vlan_proto;
  25                         __u16   vlan_tci;
  26                 };
  27         };
  28
  29 as a temporary storage for the VLAN hwaccel tag, or the DSA hwaccel tag.
  30 If this is a DSA master it's a DSA hwaccel tag, and finally clears up
  31 the skb VLAN hwaccel header.
  32
  33 I'm guessing that the problem is the (mis)use of API.
  34 skb_vlan_tag_present() looks like this:
  35
  36  #define skb_vlan_tag_present(__skb)    (!!(__skb)->vlan_all)
  37
  38 So if both vlan_proto and vlan_tci are zeroes, skb_vlan_tag_present()
  39 returns precisely false. I don't know for sure what is the format of the
  40 DSA hwaccel tag, but I surely know that lowermost 3 bits of vlan_proto
  41 are 0 when receiving from port 0:
  42
  43         unsigned int port = vlan_proto & GENMASK(2, 0);
  44
  45 If the RX descriptor has no other bits set to non-zero values in
  46 RX_DMA_VTAG, then the call to __vlan_hwaccel_put_tag() will not, in
  47 fact, make the subsequent skb_vlan_tag_present() return true, because
  48 it's implemented like this:
  49
  50 static inline void __vlan_hwaccel_put_tag(struct sk_buff *skb,
  51                                           __be16 vlan_proto, u16 vlan_tci)
  52 {
  53         skb->vlan_proto = vlan_proto;
  54         skb->vlan_tci = vlan_tci;
  55 }
  56
  57 What we need to do to fix this problem (assuming this is the problem) is
  58 to stop using skb->vlan_all as temporary storage for driver affairs, and
  59 just create some local variables that serve the same purpose, but
  60 hopefully better. Instead of calling skb_vlan_tag_present(), let's look
  61 at a boolean has_hwaccel_tag which we set to true when the RX DMA
  62 descriptors have something. Disambiguate based on netdev_uses_dsa()
  63 whether this is a VLAN or DSA hwaccel tag, and only call
  64 __vlan_hwaccel_put_tag() if we're certain it's a VLAN tag.
  65
  66 Arınç confirms that the treatment works, so this validates the
  67 assumption.
  68
  69 Link: https://lore.kernel.org/netdev/704f3a72-fc9e-714a-db54-272e17612637@arinc9.com/
  70 Fixes: 2d7605a72906 ("net: ethernet: mtk_eth_soc: enable hardware DSA untagging")
  71 Reported-by: Arınç ÜNAL <arinc.unal@arinc9.com>
  72 Tested-by: Arınç ÜNAL <arinc.unal@arinc9.com>
  73 Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
  74 Reviewed-by: Felix Fietkau <nbd@nbd.name>
  75 Signed-off-by: David S. Miller <davem@davemloft.net>
  76 ---
  77
  78 --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
  79 +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
  80 @@ -1877,7 +1877,9 @@ static int mtk_poll_rx(struct napi_struc
  81
  82         while (done < budget) {
  83                 unsigned int pktlen, *rxdcsum;
  84 +               bool has_hwaccel_tag = false;
  85                 struct net_device *netdev;
  86 +               u16 vlan_proto, vlan_tci;
  87                 dma_addr_t dma_addr;
  88                 u32 hash, reason;
  89                 int mac = 0;
  90 @@ -2017,27 +2019,29 @@ static int mtk_poll_rx(struct napi_struc
  91
  92                 if (netdev->features & NETIF_F_HW_VLAN_CTAG_RX) {
  93                         if (MTK_HAS_CAPS(eth->soc->caps, MTK_NETSYS_V2)) {
  94 -                               if (trxd.rxd3 & RX_DMA_VTAG_V2)
  95 -                                       __vlan_hwaccel_put_tag(skb,
  96 -                                               htons(RX_DMA_VPID(trxd.rxd4)),
  97 -                                               RX_DMA_VID(trxd.rxd4));
  98 +                               if (trxd.rxd3 & RX_DMA_VTAG_V2) {
  99 +                                       vlan_proto = RX_DMA_VPID(trxd.rxd4);
 100 +                                       vlan_tci = RX_DMA_VID(trxd.rxd4);
 101 +                                       has_hwaccel_tag = true;
 102 +                               }
 103                         } else if (trxd.rxd2 & RX_DMA_VTAG) {
 104 -                               __vlan_hwaccel_put_tag(skb, htons(RX_DMA_VPID(trxd.rxd3)),
 105 -                                                      RX_DMA_VID(trxd.rxd3));
 106 +                               vlan_proto = RX_DMA_VPID(trxd.rxd3);
 107 +                               vlan_tci = RX_DMA_VID(trxd.rxd3);
 108 +                               has_hwaccel_tag = true;
 109                         }
 110                 }
 111
 112                 /* When using VLAN untagging in combination with DSA, the
 113                  * hardware treats the MTK special tag as a VLAN and untags it.
 114                  */
 115 -               if (skb_vlan_tag_present(skb) && netdev_uses_dsa(netdev)) {
 116 -                       unsigned int port = ntohs(skb->vlan_proto) & GENMASK(2, 0);
 117 +               if (has_hwaccel_tag && netdev_uses_dsa(netdev)) {
 118 +                       unsigned int port = vlan_proto & GENMASK(2, 0);
 119
 120                         if (port < ARRAY_SIZE(eth->dsa_meta) &&
 121                             eth->dsa_meta[port])
 122                                 skb_dst_set_noref(skb, &eth->dsa_meta[port]->dst);
 123 -
 124 -                       __vlan_hwaccel_clear_tag(skb);
 125 +               } else if (has_hwaccel_tag) {
 126 +                       __vlan_hwaccel_put_tag(skb, htons(vlan_proto), vlan_tci);
 127                 }
 128
 129                 skb_record_rx_queue(skb, 0);