[PATCH] net/ice: add explicit control of link auto-negotiation

[Bruce Richardson <bruce.richardson@intel.com>]

When selecting a fixed speed of the link, whether or not
autonegotiation (e.g. AN Clause 37, etc.), needs to be enabled depends
on the peer link. While commit 3dc2933866d9 ("net/ice: disable link
negotiation for fixed speed selection") would allow link setup when the
remote side also has a fixed link without AN37 auto-negotiation, it
causes the link to flap up and down when e.g. two ports are connected
back to back and only one is set to a fixed speed.

Support both scenarios of auto-negotiation supported or unsupported on
the remote end by adding an explicit driver option for disabling
auto-negotiation when a fixed speed is selected. If no fixed speed
setting, then new option does nothing.

Fixes: 3dc2933866d9 ("net/ice: disable link negotiation for fixed speed selection")

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
---
 doc/guides/nics/ice.rst                | 10 ++++++++++
 doc/guides/rel_notes/release_26_11.rst |  2 ++
 drivers/net/intel/ice/ice_ethdev.c     | 12 +++++++++++-
 drivers/net/intel/ice/ice_ethdev.h     |  1 +
 4 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/doc/guides/nics/ice.rst b/doc/guides/nics/ice.rst
index ca3a94655b..af36341c9a 100644
--- a/doc/guides/nics/ice.rst
+++ b/doc/guides/nics/ice.rst
@@ -107,6 +107,16 @@ Configuration
 Runtime Configuration
 ~~~~~~~~~~~~~~~~~~~~~
 
+``auto_neg_disable`` (default ``0``)
+   Control hardware link negotiation when a fixed speed is requested with ``RTE_ETH_LINK_SPEED_FIXED``.
+   By default, the firmware's negotiation settings are preserved,
+   allowing a fixed-speed link to use negotiation such as Clause 37 when required by its peer.
+   Set ``auto_neg_disable=1`` to disable Clause 28, Clause 37 and Clause 73 negotiation.
+   This option has no effect when automatic speed selection is requested.
+   For example::
+
+      -a 80:00.0,auto_neg_disable=1
+
 - ``Safe Mode Support`` (default ``0``)
 
   If driver failed to load OS package, by default driver's initialization failed.
diff --git a/doc/guides/rel_notes/release_26_11.rst b/doc/guides/rel_notes/release_26_11.rst
index 9259954c0f..333d13c3f5 100644
--- a/doc/guides/rel_notes/release_26_11.rst
+++ b/doc/guides/rel_notes/release_26_11.rst
@@ -159,6 +159,8 @@ New Features
 
 * **Updated Intel ice driver.**
 
+  * Added ``auto_neg_disable`` devarg to disable hardware link negotiation for fixed-speed links.
+    By default, fixed-speed links now preserve the firmware's negotiation settings.
   * Added chip temperature to the extended statistics.
   * Added Tx context descriptor support to the AVX2 and AVX512 vector Tx paths,
     enabling QinQ tag insertion and outer IPv4/UDP checksum offloads on those paths.
diff --git a/drivers/net/intel/ice/ice_ethdev.c b/drivers/net/intel/ice/ice_ethdev.c
index d6dfc07ad5..f9c719163d 100644
--- a/drivers/net/intel/ice/ice_ethdev.c
+++ b/drivers/net/intel/ice/ice_ethdev.c
@@ -45,6 +45,7 @@
 #define ICE_RL_BURST_SIZE_ARG     "rl_burst_size"
 #define ICE_SOURCE_PRUNE_ARG      "source-prune"
 #define ICE_LINK_STATE_ON_CLOSE   "link_state_on_close"
+#define ICE_AUTO_NEG_DISABLE_ARG  "auto_neg_disable"
 
 #define ICE_CYCLECOUNTER_MASK  0xffffffffffffffffULL
 
@@ -64,6 +65,7 @@ static const char * const ice_valid_args[] = {
 	ICE_RL_BURST_SIZE_ARG,
 	ICE_SOURCE_PRUNE_ARG,
 	ICE_LINK_STATE_ON_CLOSE,
+	ICE_AUTO_NEG_DISABLE_ARG,
 	NULL
 };
 
@@ -2541,6 +2543,11 @@ static int ice_parse_devargs(struct rte_eth_dev *dev)
 
 	ret = rte_kvargs_process(kvlist, ICE_LINK_STATE_ON_CLOSE,
 				 &parse_link_state_on_close, &ad->devargs.link_state_on_close);
+	if (ret)
+		goto bail;
+
+	ret = rte_kvargs_process(kvlist, ICE_AUTO_NEG_DISABLE_ARG,
+				 &parse_bool, &ad->devargs.auto_neg_disable);
 
 bail:
 	rte_kvargs_free(kvlist);
@@ -5225,6 +5232,7 @@ static int
 ice_apply_link_speed(struct rte_eth_dev *dev)
 {
 	uint16_t speed;
+	const struct ice_adapter *ad = ICE_DEV_PRIVATE_TO_ADAPTER(dev->data->dev_private);
 	struct ice_hw *hw = ICE_DEV_PRIVATE_TO_HW(dev->data->dev_private);
 	struct rte_eth_conf *conf = &dev->data->dev_conf;
 
@@ -5247,7 +5255,8 @@ ice_apply_link_speed(struct rte_eth_dev *dev)
 		return -EINVAL;
 	}
 
-	bool link_autoneg = (conf->link_speeds & RTE_ETH_LINK_SPEED_FIXED) == 0;
+	const bool link_autoneg = !ad->devargs.auto_neg_disable ||
+			(conf->link_speeds & RTE_ETH_LINK_SPEED_FIXED) == 0;
 	return ice_phy_conf_link(hw, speed, true, link_autoneg);
 }
 
@@ -8197,6 +8206,7 @@ RTE_PMD_REGISTER_PARAM_STRING(net_ice,
 			      ICE_RL_BURST_SIZE_ARG "=<N>"
 			      ICE_SOURCE_PRUNE_ARG "=<0|1>"
 			      ICE_RX_LOW_LATENCY_ARG "=<0|1>"
+			      ICE_AUTO_NEG_DISABLE_ARG "=<0|1>"
 			      ICE_LINK_STATE_ON_CLOSE "=<down|up|initial>");
 
 RTE_LOG_REGISTER_SUFFIX(ice_logtype_init, init, NOTICE);
diff --git a/drivers/net/intel/ice/ice_ethdev.h b/drivers/net/intel/ice/ice_ethdev.h
index 945e765c2c..747c003bb3 100644
--- a/drivers/net/intel/ice/ice_ethdev.h
+++ b/drivers/net/intel/ice/ice_ethdev.h
@@ -634,6 +634,7 @@ struct ice_pf {
 struct ice_devargs {
 	bool rx_low_latency;
 	bool safe_mode_support;
+	bool auto_neg_disable;
 	uint8_t proto_xtr_dflt;
 	bool default_mac_disable;
 	uint8_t proto_xtr[ICE_MAX_QUEUE_NUM];
-- 
2.55.0