[PATCH net-next v2] net: mana: Cache MANA_QUERY_LINK_CONFIG result to avoid repeated HWC queries

[Erni Sri Satya Vennela <ernis@linux.microsoft.com>]

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>
---
Changes in v2:
* Use netdev_lock() instead of introducing new per-port mutex.
* Update commit message.
---
 drivers/net/ethernet/microsoft/mana/mana_en.c | 23 +++++++++++++++----
 include/net/mana/mana.h                       |  4 ++++
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
index db14357d3732..af2517a27aad 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
@@ -1456,6 +1456,12 @@ int mana_query_link_cfg(struct mana_port_context *apc)
 	struct mana_query_link_config_req req = {};
 	int err;
 
+	netdev_assert_locked(ndev);
+
+	err = apc->link_cfg_error;
+	if (err <= 0)
+		return err;
+
 	mana_gd_init_req_hdr(&req.hdr, MANA_QUERY_LINK_CONFIG,
 			     sizeof(req), sizeof(resp));
 
@@ -1468,6 +1474,7 @@ int mana_query_link_cfg(struct mana_port_context *apc)
 	if (err) {
 		if (err == -EOPNOTSUPP) {
 			netdev_info_once(ndev, "MANA_QUERY_LINK_CONFIG not supported\n");
+			apc->link_cfg_error = err;
 			return err;
 		}
 		netdev_err(ndev, "Failed to query link config: %d\n", err);
@@ -1485,12 +1492,12 @@ int mana_query_link_cfg(struct mana_port_context *apc)
 		return err;
 	}
 
-	if (resp.qos_unconfigured) {
-		err = -EINVAL;
-		return err;
-	}
+	if (resp.qos_unconfigured)
+		return -EINVAL;
+
 	apc->speed = resp.link_speed_mbps;
 	apc->max_speed = resp.qos_speed_mbps;
+	apc->link_cfg_error = 0;
 	return 0;
 }
 
@@ -1502,6 +1509,8 @@ int mana_set_bw_clamp(struct mana_port_context *apc, u32 speed,
 	struct net_device *ndev = apc->ndev;
 	int err;
 
+	netdev_assert_locked(ndev);
+
 	mana_gd_init_req_hdr(&req.hdr, MANA_SET_BW_CLAMP,
 			     sizeof(req), sizeof(resp));
 	req.vport = apc->port_handle;
@@ -1535,6 +1544,8 @@ int mana_set_bw_clamp(struct mana_port_context *apc, u32 speed,
 	if (resp.qos_unconfigured)
 		netdev_info(ndev, "QoS is unconfigured\n");
 
+	/* Invalidate the cache; next query will re-fetch from firmware. */
+	apc->link_cfg_error = 1;
 	return 0;
 }
 
@@ -3448,6 +3459,7 @@ static int mana_probe_port(struct mana_context *ac, int port_idx,
 	apc->port_handle = INVALID_MANA_HANDLE;
 	apc->pf_filter_handle = INVALID_MANA_HANDLE;
 	apc->port_idx = port_idx;
+	apc->link_cfg_error = 1;
 	apc->cqe_coalescing_enable = 0;
 
 	mutex_init(&apc->vport_mutex);
@@ -3768,6 +3780,9 @@ int mana_probe(struct gdma_dev *gd, bool resuming)
 			rtnl_lock();
 			apc = netdev_priv(ac->ports[i]);
 			enable_work(&apc->queue_reset_work);
+			netdev_lock(ac->ports[i]);
+			apc->link_cfg_error = 1;
+			netdev_unlock(ac->ports[i]);
 			err = mana_attach(ac->ports[i]);
 			rtnl_unlock();
 			/* Log the port for which the attach failed, stop
diff --git a/include/net/mana/mana.h b/include/net/mana/mana.h
index d9c27310fd04..2a45ff7211ef 100644
--- a/include/net/mana/mana.h
+++ b/include/net/mana/mana.h
@@ -555,6 +555,10 @@ 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 */
-- 
2.34.1