[PATCH 3/3] net: microchip_t1s: conditional collision detection

["Ramón N.Rodriguez" <ramon.nordin.rodriguez@ferroamp.se>]

From: Ramón Nordin Rodriguez <ramon.nordin.rodriguez@ferroamp.se>

This commit conditionally sets the collision detection bit on lan867x
and lan865x phys on changing PLCA enabled on/off. The intended realworld
scenario is that all nodes on the network run the same settings with
regards to plca, and when plca is enabled the physical layer guarantees
that no collisions should occur.
In a practical setting where it was tested running one node with
collision detection on and other off, the node with collision detection
on dropped a lot of packets, leading to a poor performing link.
Worth noting here is that the phys default/reset to plca disabled and
collision detection enabled. Thus this change would only have an effect
when changing settings via ethtool.

Signed-off-by: Ramón Nordin Rodriguez <ramon.nordin.rodriguez@ferroamp.se>
---
 drivers/net/phy/microchip_t1s.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/drivers/net/phy/microchip_t1s.c b/drivers/net/phy/microchip_t1s.c
index db84d850b165..3b1e82ecdf69 100644
--- a/drivers/net/phy/microchip_t1s.c
+++ b/drivers/net/phy/microchip_t1s.c
@@ -23,8 +23,10 @@
 #define LAN865X_REG_CFGPARAM_DATA 0x00D9
 #define LAN865X_REG_CFGPARAM_CTRL 0x00DA
 #define LAN865X_REG_STS2 0x0019
+#define LAN86XX_REG_COLLISION_DETECT 0x0087
 
 #define LAN865X_CFGPARAM_READ_ENABLE BIT(1)
+#define LAN86XX_COLLISION_DETECT_ENABLE BIT(15)
 
 /* The arrays below are pulled from the following table from AN1699
  * Access MMD Address Value Mask
@@ -363,6 +365,27 @@ static int lan86xx_read_status(struct phy_device *phydev)
 	return 0;
 }
 
+static int lan86xx_plca_set_cfg(struct phy_device *phydev,
+				const struct phy_plca_cfg *plca_cfg)
+{
+	int err;
+
+	err = genphy_c45_plca_set_cfg(phydev, plca_cfg);
+	if (err)
+		return err;
+
+	/* Disable collision detect on the phy when PLCA is enabled.
+	 * Noise can be picked up as a false positive for collisions
+	 * leading to the phy dropping legitimate packets.
+	 * No collisions should be possible when all nodes are setup
+	 * for running PLCA.
+	 */
+	return phy_modify_mmd(phydev, MDIO_MMD_VEND2,
+			LAN86XX_REG_COLLISION_DETECT,
+			LAN86XX_COLLISION_DETECT_ENABLE,
+			plca_cfg->enabled ? 0 : LAN86XX_COLLISION_DETECT_ENABLE);
+}
+
 static struct phy_driver microchip_t1s_driver[] = {
 	{
 		PHY_ID_MATCH_EXACT(PHY_ID_LAN867X_REVB1),
@@ -371,7 +394,7 @@ static struct phy_driver microchip_t1s_driver[] = {
 		.config_init        = lan867x_revb1_config_init,
 		.read_status        = lan86xx_read_status,
 		.get_plca_cfg	    = genphy_c45_plca_get_cfg,
-		.set_plca_cfg	    = genphy_c45_plca_set_cfg,
+		.set_plca_cfg	    = lan86xx_plca_set_cfg,
 		.get_plca_status    = genphy_c45_plca_get_status,
 	},
 	{
@@ -381,7 +404,7 @@ static struct phy_driver microchip_t1s_driver[] = {
 		.config_init        = lan867x_revc1_config_init,
 		.read_status        = lan86xx_read_status,
 		.get_plca_cfg	    = genphy_c45_plca_get_cfg,
-		.set_plca_cfg	    = genphy_c45_plca_set_cfg,
+		.set_plca_cfg	    = lan86xx_plca_set_cfg,
 		.get_plca_status    = genphy_c45_plca_get_status,
 	},
 	{
@@ -391,7 +414,7 @@ static struct phy_driver microchip_t1s_driver[] = {
 		.config_init        = lan865x_revb0_config_init,
 		.read_status        = lan86xx_read_status,
 		.get_plca_cfg	    = genphy_c45_plca_get_cfg,
-		.set_plca_cfg	    = genphy_c45_plca_set_cfg,
+		.set_plca_cfg	    = lan86xx_plca_set_cfg,
 		.get_plca_status    = genphy_c45_plca_get_status,
 	},
 };
-- 
2.40.1