--- /dev/null
+From b79d7c14f48083abb3fb061370c0c64a569edf4c Mon Sep 17 00:00:00 2001
+From: Vladimir Oltean <olteanv@gmail.com>
+Date: Sat, 17 Jun 2023 09:26:48 +0300
+Subject: net: dsa: introduce preferred_default_local_cpu_port and use on MT7530
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+From: Vladimir Oltean <olteanv@gmail.com>
+
+commit b79d7c14f48083abb3fb061370c0c64a569edf4c upstream.
+
+Since the introduction of the OF bindings, DSA has always had a policy that
+in case multiple CPU ports are present in the device tree, the numerically
+smallest one is always chosen.
+
+The MT7530 switch family, except the switch on the MT7988 SoC, has 2 CPU
+ports, 5 and 6, where port 6 is preferable on the MT7531BE switch because
+it has higher bandwidth.
+
+The MT7530 driver developers had 3 options:
+- to modify DSA when the MT7531 switch support was introduced, such as to
+ prefer the better port
+- to declare both CPU ports in device trees as CPU ports, and live with the
+ sub-optimal performance resulting from not preferring the better port
+- to declare just port 6 in the device tree as a CPU port
+
+Of course they chose the path of least resistance (3rd option), kicking the
+can down the road. The hardware description in the device tree is supposed
+to be stable - developers are not supposed to adopt the strategy of
+piecemeal hardware description, where the device tree is updated in
+lockstep with the features that the kernel currently supports.
+
+Now, as a result of the fact that they did that, any attempts to modify the
+device tree and describe both CPU ports as CPU ports would make DSA change
+its default selection from port 6 to 5, effectively resulting in a
+performance degradation visible to users with the MT7531BE switch as can be
+seen below.
+
+Without preferring port 6:
+
+[ ID][Role] Interval Transfer Bitrate Retr
+[ 5][TX-C] 0.00-20.00 sec 374 MBytes 157 Mbits/sec 734 sender
+[ 5][TX-C] 0.00-20.00 sec 373 MBytes 156 Mbits/sec receiver
+[ 7][RX-C] 0.00-20.00 sec 1.81 GBytes 778 Mbits/sec 0 sender
+[ 7][RX-C] 0.00-20.00 sec 1.81 GBytes 777 Mbits/sec receiver
+
+With preferring port 6:
+
+[ ID][Role] Interval Transfer Bitrate Retr
+[ 5][TX-C] 0.00-20.00 sec 1.99 GBytes 856 Mbits/sec 273 sender
+[ 5][TX-C] 0.00-20.00 sec 1.99 GBytes 855 Mbits/sec receiver
+[ 7][RX-C] 0.00-20.00 sec 1.72 GBytes 737 Mbits/sec 15 sender
+[ 7][RX-C] 0.00-20.00 sec 1.71 GBytes 736 Mbits/sec receiver
+
+Using one port for WAN and the other ports for LAN is a very popular use
+case which is what this test emulates.
+
+As such, this change proposes that we retroactively modify stable kernels
+(which don't support the modification of the CPU port assignments, so as to
+let user space fix the problem and restore the throughput) to keep the
+mt7530 driver preferring port 6 even with device trees where the hardware
+is more fully described.
+
+Fixes: c288575f7810 ("net: dsa: mt7530: Add the support of MT7531 switch")
+Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
+Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
+Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
+Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ drivers/net/dsa/mt7530.c | 15 +++++++++++++++
+ include/net/dsa.h | 8 ++++++++
+ net/dsa/dsa2.c | 24 +++++++++++++++++++++++-
+ 3 files changed, 46 insertions(+), 1 deletion(-)
+
+--- a/drivers/net/dsa/mt7530.c
++++ b/drivers/net/dsa/mt7530.c
+@@ -419,6 +419,20 @@ static void mt7530_pll_setup(struct mt75
+ core_set(priv, CORE_TRGMII_GSW_CLK_CG, REG_GSWCK_EN);
+ }
+
++/* If port 6 is available as a CPU port, always prefer that as the default,
++ * otherwise don't care.
++ */
++static struct dsa_port *
++mt753x_preferred_default_local_cpu_port(struct dsa_switch *ds)
++{
++ struct dsa_port *cpu_dp = dsa_to_port(ds, 6);
++
++ if (dsa_port_is_cpu(cpu_dp))
++ return cpu_dp;
++
++ return NULL;
++}
++
+ /* Setup port 6 interface mode and TRGMII TX circuit */
+ static int
+ mt7530_pad_clk_setup(struct dsa_switch *ds, phy_interface_t interface)
+@@ -3405,6 +3419,7 @@ static int mt753x_set_mac_eee(struct dsa
+ static const struct dsa_switch_ops mt7530_switch_ops = {
+ .get_tag_protocol = mtk_get_tag_protocol,
+ .setup = mt753x_setup,
++ .preferred_default_local_cpu_port = mt753x_preferred_default_local_cpu_port,
+ .get_strings = mt7530_get_strings,
+ .get_ethtool_stats = mt7530_get_ethtool_stats,
+ .get_sset_count = mt7530_get_sset_count,
+--- a/include/net/dsa.h
++++ b/include/net/dsa.h
+@@ -969,6 +969,14 @@ struct dsa_switch_ops {
+ void (*port_disable)(struct dsa_switch *ds, int port);
+
+ /*
++ * Compatibility between device trees defining multiple CPU ports and
++ * drivers which are not OK to use by default the numerically smallest
++ * CPU port of a switch for its local ports. This can return NULL,
++ * meaning "don't know/don't care".
++ */
++ struct dsa_port *(*preferred_default_local_cpu_port)(struct dsa_switch *ds);
++
++ /*
+ * Port's MAC EEE settings
+ */
+ int (*set_mac_eee)(struct dsa_switch *ds, int port,
+--- a/net/dsa/dsa2.c
++++ b/net/dsa/dsa2.c
+@@ -425,6 +425,24 @@ static int dsa_tree_setup_default_cpu(st
+ return 0;
+ }
+
++static struct dsa_port *
++dsa_switch_preferred_default_local_cpu_port(struct dsa_switch *ds)
++{
++ struct dsa_port *cpu_dp;
++
++ if (!ds->ops->preferred_default_local_cpu_port)
++ return NULL;
++
++ cpu_dp = ds->ops->preferred_default_local_cpu_port(ds);
++ if (!cpu_dp)
++ return NULL;
++
++ if (WARN_ON(!dsa_port_is_cpu(cpu_dp) || cpu_dp->ds != ds))
++ return NULL;
++
++ return cpu_dp;
++}
++
+ /* Perform initial assignment of CPU ports to user ports and DSA links in the
+ * fabric, giving preference to CPU ports local to each switch. Default to
+ * using the first CPU port in the switch tree if the port does not have a CPU
+@@ -432,12 +450,16 @@ static int dsa_tree_setup_default_cpu(st
+ */
+ static int dsa_tree_setup_cpu_ports(struct dsa_switch_tree *dst)
+ {
+- struct dsa_port *cpu_dp, *dp;
++ struct dsa_port *preferred_cpu_dp, *cpu_dp, *dp;
+
+ list_for_each_entry(cpu_dp, &dst->ports, list) {
+ if (!dsa_port_is_cpu(cpu_dp))
+ continue;
+
++ preferred_cpu_dp = dsa_switch_preferred_default_local_cpu_port(cpu_dp->ds);
++ if (preferred_cpu_dp && preferred_cpu_dp != cpu_dp)
++ continue;
++
+ /* Prefer a local CPU port */
+ dsa_switch_for_each_port(dp, cpu_dp->ds) {
+ /* Prefer the first local CPU port found */
projects / thirdparty / kernel / stable-queue.git / blobdiff