net: mana: Cache MANA_QUERY_LINK_CONFIG result to avoid repeated HWC queries

mana_query_link_cfg() sends an HWC command to firmware on every call,
but the link speed and QoS values it returns only change when the
driver explicitly calls mana_set_bw_clamp(). This function is called
not only by userspace via ethtool get_link_ksettings, but also
periodically by hv_netvsc through netvsc_get_link_ksettings and by
the sysfs speed_show attribute via dev_attr_show, resulting in
unnecessary HWC traffic every few minutes.

Add a link_cfg_error field to mana_port_context to cache the query
result. The field uses three states: 1 (not yet queried, initial
value set during mana_probe_port), 0 (success, speed/max_speed are
valid), or a negative errno for permanent errors like -EOPNOTSUPP
when the hardware does not support the command. Transient errors and
qos_unconfigured responses are not cached so that subsequent calls
will retry.

MANA is ops-locked because it implements net_shaper_ops, so the core
already takes netdev_lock() around all ethtool_ops and net_shaper_ops
entry points. Reuse that lock to serialize mana_query_link_cfg() and
mana_set_bw_clamp(). This prevents a concurrent mana_set_bw_clamp()
from racing with an in-flight query and publishing stale pre-clamp
speed/max_speed.

Invalidate the cache inside mana_set_bw_clamp() on success, so all
current and future callers that change the link configuration
automatically trigger a fresh query on the next mana_query_link_cfg()
call. Also reset link_cfg_error during resume in mana_probe() under
netdev_lock(), so that any query already in flight cannot later
store 0 and silently overwrite the post-resume invalidation.

Signed-off-by: Erni Sri Satya Vennela <ernis@linux.microsoft.com>
Link: https://patch.msgid.link/20260606133301.2180073-1-ernis@linux.microsoft.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/net/mana/mana.h b/include/net/mana/mana.h
index 5a9b94e0ef34..13c87baf018e 100644
--- a/include/net/mana/mana.h
+++ b/include/net/mana/mana.h
@@ -562,6 +562,10 @@ struct mana_port_context {
 	u32 speed;
 	/* Maximum speed supported by the SKU (mbps) */
 	u32 max_speed;
+	/* 1 = not queried, 0 = cached success, negative = permanent error.
+	 * Protected by the netdev instance lock.
+	 */
+	int link_cfg_error;
 
 	bool port_is_up;
 	bool port_st_save; /* Saved port state */