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authorVladimir Oltean <olteanv@gmail.com>2023-06-17 09:26:48 +0300
committerDavid S. Miller <davem@davemloft.net>2023-06-20 11:40:26 +0300
commitb79d7c14f48083abb3fb061370c0c64a569edf4c (patch)
treed4980e1dadf47187a3e855c153a2fe11c1576917 /net/dsa
parent8332cf6fd7c7087dbc2067115b33979c9851bbc4 (diff)
downloadlinux-b79d7c14f48083abb3fb061370c0c64a569edf4c.tar.xz
net: dsa: introduce preferred_default_local_cpu_port and use on MT7530
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>
Diffstat (limited to 'net/dsa')
-rw-r--r--net/dsa/dsa.c24
1 files changed, 23 insertions, 1 deletions
diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
index ab1afe67fd18..1afed89e03c0 100644
--- a/net/dsa/dsa.c
+++ b/net/dsa/dsa.c
@@ -403,6 +403,24 @@ static int dsa_tree_setup_default_cpu(struct dsa_switch_tree *dst)
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
@@ -410,12 +428,16 @@ static int dsa_tree_setup_default_cpu(struct dsa_switch_tree *dst)
*/
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 */