generic: mt7530: backport support for the MT7988 built-in switch

Backport commits adding support for the MT7988 built-in switch to the
mt7530 driver.

This change results in the Kconfig symbol NET_DSA_MT7530 to be extended
by NET_DSA_MT7530_MDIO (everything formally covered by NET_DSA_MT7530)
and NET_DSA_MT7530_MMIO (a new driver for the MMIO-connected built-in
switch of the MT7988 SoC).

Select NET_DSA_MT7530_MDIO for all targets previously selecting
NET_DSA_MT7530, with the exception of mediatek/filogic which also
selects NET_DSA_MT7530_MMIO.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit 958fdf36e35c814eb83faf2c39db4ca379c921b5)

1 files changed, 47 insertions, 0 deletions

diff --git a/target/linux/generic/backport-5.15/790-v6.4-0012-net-dsa-mt7530-skip-locking-if-MDIO-bus-isn-t-presen.patch b/target/linux/generic/backport-5.15/790-v6.4-0012-net-dsa-mt7530-skip-locking-if-MDIO-bus-isn-t-presen.patch
new file mode 100644
index 0000000000..95b7cc6afe
--- /dev/null
+++ b/target/linux/generic/backport-5.15/790-v6.4-0012-net-dsa-mt7530-skip-locking-if-MDIO-bus-isn-t-presen.patch
@@ -0,0 +1,47 @@
+From 54d4147a121cec5004a673a58572da346e4458f8 Mon Sep 17 00:00:00 2001
+From: Daniel Golle <daniel@makrotopia.org>
+Date: Mon, 3 Apr 2023 02:19:28 +0100
+Subject: [PATCH 15/16] net: dsa: mt7530: skip locking if MDIO bus isn't
+ present
+
+As MT7530 and MT7531 internally use 32-bit wide registers, each access
+to any register of the switch requires several operations on the MDIO
+bus. Hence if there is congruent access, e.g. due to PCS or PHY
+polling, this can mess up and interfere with another ongoing register
+access sequence.
+
+However, the MDIO bus mutex is only relevant for MDIO-connected
+switches. Prepare switches which have there registers directly mapped
+into the SoCs register space via MMIO which do not require such
+locking. There we can simply use regmap's default locking mechanism.
+
+Hence guard mutex operations to only be performed in case of MDIO
+connected switches.
+
+Signed-off-by: Daniel Golle <daniel@makrotopia.org>
+Reviewed-by: Andrew Lunn <andrew@lunn.ch>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/dsa/mt7530.c | 6 ++++--
+ 1 file changed, 4 insertions(+), 2 deletions(-)
+
+--- a/drivers/net/dsa/mt7530.c
++++ b/drivers/net/dsa/mt7530.c
+@@ -144,13 +144,15 @@ err:
+ static void
+ mt7530_mutex_lock(struct mt7530_priv *priv)
+ {
+-	mutex_lock_nested(&priv->bus->mdio_lock, MDIO_MUTEX_NESTED);
++	if (priv->bus)
++		mutex_lock_nested(&priv->bus->mdio_lock, MDIO_MUTEX_NESTED);
+ }
+ 
+ static void
+ mt7530_mutex_unlock(struct mt7530_priv *priv)
+ {
+-	mutex_unlock(&priv->bus->mdio_lock);
++	if (priv->bus)
++		mutex_unlock(&priv->bus->mdio_lock);
+ }
+ 
+ static void