git.openwrt.org Git - openwrt/staging/pepe2k.git/blob

   1 From 06efc9b8a1360cad83cae6e71558e5458cc1fbf3 Mon Sep 17 00:00:00 2001
   2 From: Vladimir Oltean <vladimir.oltean@nxp.com>
   3 Date: Tue, 29 Nov 2022 16:12:14 +0200
   4 Subject: [PATCH 07/14] net: dpaa2-eth: assign priv->mac after
   5  dpaa2_mac_connect() call
   6
   7 There are 2 requirements for correct code:
   8
   9 - Any time the driver accesses the priv->mac pointer at runtime, it
  10   either holds NULL to indicate a DPNI-DPNI connection (or unconnected
  11   DPNI), or a struct dpaa2_mac whose phylink instance was fully
  12   initialized (created and connected to the PHY). No changes are made to
  13   priv->mac while it is being used. Currently, rtnl_lock() watches over
  14   the call to dpaa2_eth_connect_mac(), so it serves the purpose of
  15   serializing this with all readers of priv->mac.
  16
  17 - dpaa2_mac_connect() should run unlocked, because inside it are 2
  18   phylink calls with incompatible locking requirements: phylink_create()
  19   requires that the rtnl_mutex isn't held, and phylink_fwnode_phy_connect()
  20   requires that the rtnl_mutex is held. The only way to solve those
  21   contradictory requirements is to let dpaa2_mac_connect() take
  22   rtnl_lock() when it needs to.
  23
  24 To solve both requirements, we need to identify the writer side of the
  25 priv->mac pointer, which can be wrapped in a mutex private to the driver
  26 in a future patch. The dpaa2_mac_connect() cannot be part of the writer
  27 side critical section, because of an AB/BA deadlock with rtnl_lock().
  28
  29 So the strategy needs to be that where we prepare the DPMAC by calling
  30 dpaa2_mac_connect(), and only make priv->mac point to it once it's fully
  31 prepared. This ensures that the writer side critical section has the
  32 absolute minimum surface it can.
  33
  34 The reverse strategy is adopted in the dpaa2_eth_disconnect_mac() code
  35 path. This makes sure that priv->mac is NULL when we start tearing down
  36 the DPMAC that we disconnected from, and concurrent code will simply not
  37 see it.
  38
  39 No locking changes in this patch (concurrent code is still blocked by
  40 the rtnl_mutex).
  41
  42 Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
  43 Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>
  44 Tested-by: Ioana Ciornei <ioana.ciornei@nxp.com>
  45 Signed-off-by: Paolo Abeni <pabeni@redhat.com>
  46 ---
  47  .../net/ethernet/freescale/dpaa2/dpaa2-eth.c  | 21 +++++++++++--------
  48  1 file changed, 12 insertions(+), 9 deletions(-)
  49
  50 --- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
  51 +++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
  52 @@ -4444,9 +4444,8 @@ static int dpaa2_eth_connect_mac(struct
  53         err = dpaa2_mac_open(mac);
  54         if (err)
  55                 goto err_free_mac;
  56 -       priv->mac = mac;
  57
  58 -       if (dpaa2_eth_is_type_phy(priv)) {
  59 +       if (dpaa2_mac_is_type_phy(mac)) {
  60                 err = dpaa2_mac_connect(mac);
  61                 if (err && err != -EPROBE_DEFER)
  62                         netdev_err(priv->net_dev, "Error connecting to the MAC endpoint: %pe",
  63 @@ -4455,11 +4454,12 @@ static int dpaa2_eth_connect_mac(struct
  64                         goto err_close_mac;
  65         }
  66
  67 +       priv->mac = mac;
  68 +
  69         return 0;
  70
  71  err_close_mac:
  72         dpaa2_mac_close(mac);
  73 -       priv->mac = NULL;
  74  err_free_mac:
  75         kfree(mac);
  76         return err;
  77 @@ -4467,15 +4467,18 @@ err_free_mac:
  78
  79  static void dpaa2_eth_disconnect_mac(struct dpaa2_eth_priv *priv)
  80  {
  81 -       if (dpaa2_eth_is_type_phy(priv))
  82 -               dpaa2_mac_disconnect(priv->mac);
  83 +       struct dpaa2_mac *mac = priv->mac;
  84 +
  85 +       priv->mac = NULL;
  86
  87 -       if (!dpaa2_eth_has_mac(priv))
  88 +       if (!mac)
  89                 return;
  90
  91 -       dpaa2_mac_close(priv->mac);
  92 -       kfree(priv->mac);
  93 -       priv->mac = NULL;
  94 +       if (dpaa2_mac_is_type_phy(mac))
  95 +               dpaa2_mac_disconnect(mac);
  96 +
  97 +       dpaa2_mac_close(mac);
  98 +       kfree(mac);
  99  }
 100
 101  static irqreturn_t dpni_irq0_handler_thread(int irq_num, void *arg)