target/linux/generic/backport-6.1/790-13-v6.4-net-dsa-mt7530-skip-locking-if-MDIO-bus-isn-t-presen.patch

   1 From 86e1168a214b7ab0883acf1e7a6885a7a949e3e7 Mon Sep 17 00:00:00 2001
   2 From: Daniel Golle <daniel@makrotopia.org>
   3 Date: Mon, 3 Apr 2023 02:19:28 +0100
   4 Subject: [PATCH 13/48] net: dsa: mt7530: skip locking if MDIO bus isn't
   5  present
   6
   7 As MT7530 and MT7531 internally use 32-bit wide registers, each access
   8 to any register of the switch requires several operations on the MDIO
   9 bus. Hence if there is congruent access, e.g. due to PCS or PHY
  10 polling, this can mess up and interfere with another ongoing register
  11 access sequence.
  12
  13 However, the MDIO bus mutex is only relevant for MDIO-connected
  14 switches. Prepare switches which have there registers directly mapped
  15 into the SoCs register space via MMIO which do not require such
  16 locking. There we can simply use regmap's default locking mechanism.
  17
  18 Hence guard mutex operations to only be performed in case of MDIO
  19 connected switches.
  20
  21 Signed-off-by: Daniel Golle <daniel@makrotopia.org>
  22 Reviewed-by: Andrew Lunn <andrew@lunn.ch>
  23 Signed-off-by: David S. Miller <davem@davemloft.net>
  24 ---
  25  drivers/net/dsa/mt7530.c | 6 ++++--
  26  1 file changed, 4 insertions(+), 2 deletions(-)
  27
  28 --- a/drivers/net/dsa/mt7530.c
  29 +++ b/drivers/net/dsa/mt7530.c
  30 @@ -144,13 +144,15 @@ err:
  31  static void
  32  mt7530_mutex_lock(struct mt7530_priv *priv)
  33  {
  34 -       mutex_lock_nested(&priv->bus->mdio_lock, MDIO_MUTEX_NESTED);
  35 +       if (priv->bus)
  36 +               mutex_lock_nested(&priv->bus->mdio_lock, MDIO_MUTEX_NESTED);
  37  }
  38
  39  static void
  40  mt7530_mutex_unlock(struct mt7530_priv *priv)
  41  {
  42 -       mutex_unlock(&priv->bus->mdio_lock);
  43 +       if (priv->bus)
  44 +               mutex_unlock(&priv->bus->mdio_lock);
  45  }
  46
  47  static void