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authorVladimir Oltean <vladimir.oltean@nxp.com>2020-03-27 21:55:42 +0200
committerDavid S. Miller <davem@davemloft.net>2020-03-27 16:07:24 -0700
commitbfcb813203e619a8960a819bf533ad2a108d8105 (patch)
tree835fc6a0c4048c03100f0886f4b4a2ee56a7428d /include/net
parent8c7da63978f1672eb4037bbca6e7eac73f908f03 (diff)
net: dsa: configure the MTU for switch ports
It is useful be able to configure port policers on a switch to accept frames of various sizes: - Increase the MTU for better throughput from the default of 1500 if it is known that there is no 10/100 Mbps device in the network. - Decrease the MTU to limit the latency of high-priority frames under congestion, or work around various network segments that add extra headers to packets which can't be fragmented. For DSA slave ports, this is mostly a pass-through callback, called through the regular ndo ops and at probe time (to ensure consistency across all supported switches). The CPU port is called with an MTU equal to the largest configured MTU of the slave ports. The assumption is that the user might want to sustain a bidirectional conversation with a partner over any switch port. The DSA master is configured the same as the CPU port, plus the tagger overhead. Since the MTU is by definition L2 payload (sans Ethernet header), it is up to each individual driver to figure out if it needs to do anything special for its frame tags on the CPU port (it shouldn't except in special cases). So the MTU does not contain the tagger overhead on the CPU port. However the MTU of the DSA master, minus the tagger overhead, is used as a proxy for the MTU of the CPU port, which does not have a net device. This is to avoid uselessly calling the .change_mtu function on the CPU port when nothing should change. So it is safe to assume that the DSA master and the CPU port MTUs are apart by exactly the tagger's overhead in bytes. Some changes were made around dsa_master_set_mtu(), function which was now removed, for 2 reasons: - dev_set_mtu() already calls dev_validate_mtu(), so it's redundant to do the same thing in DSA - __dev_set_mtu() returns 0 if ops->ndo_change_mtu is an absent method That is to say, there's no need for this function in DSA, we can safely call dev_set_mtu() directly, take the rtnl lock when necessary, and just propagate whatever errors get reported (since the user probably wants to be informed). Some inspiration (mainly in the MTU DSA notifier) was taken from a vaguely similar patch from Murali and Florian, who are credited as co-developers down below. Co-developed-by: Murali Krishna Policharla <murali.policharla@broadcom.com> Signed-off-by: Murali Krishna Policharla <murali.policharla@broadcom.com> Co-developed-by: Florian Fainelli <f.fainelli@gmail.com> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net')
-rw-r--r--include/net/dsa.h10
1 files changed, 10 insertions, 0 deletions
diff --git a/include/net/dsa.h b/include/net/dsa.h
index beeb81a532e3..8fc34d70a77d 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -579,6 +579,16 @@ struct dsa_switch_ops {
struct devlink_param_gset_ctx *ctx);
int (*devlink_param_set)(struct dsa_switch *ds, u32 id,
struct devlink_param_gset_ctx *ctx);
+
+ /*
+ * MTU change functionality. Switches can also adjust their MRU through
+ * this method. By MTU, one understands the SDU (L2 payload) length.
+ * If the switch needs to account for the DSA tag on the CPU port, this
+ * method needs to to do so privately.
+ */
+ int (*port_change_mtu)(struct dsa_switch *ds, int port,
+ int new_mtu);
+ int (*port_max_mtu)(struct dsa_switch *ds, int port);
};
#define DSA_DEVLINK_PARAM_DRIVER(_id, _name, _type, _cmodes) \