netdev - [PATCH net v2] phy: avoid unnecessary link-up delay in polling mode

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Date:   Wed, 29 Jan 2020 13:19:55 +0100
From:   Petr Oros <poros@...hat.com>
To:     netdev@...r.kernel.org
Cc:     andrew@...n.ch, f.fainelli@...il.com, hkallweit1@...il.com,
        ivecera@...hat.com
Subject: [PATCH net v2] phy: avoid unnecessary link-up delay in polling mode

commit 93c0970493c71f ("net: phy: consider latched link-down status in
polling mode") removed double-read of latched link-state register for
polling mode from genphy_update_link(). This added extra ~1s delay into
sequence link down->up.
Following scenario:
 - After boot link goes up
 - phy_start() is called triggering an aneg restart, hence link goes
   down and link-down info is latched.
 - After aneg has finished link goes up. In phy_state_machine is checked
   link state but it is latched "link is down". The state machine is
   scheduled after one second and there is detected "link is up". This
   extra delay can be avoided when we keep link-state register double read
   in case when link was down previously.

With this solution we don't miss a link-down event in polling mode and
link-up is faster.

Changes in v2:
- Fixed typos in phy_polling_mode() argument

Fixes: 93c0970493c71f ("net: phy: consider latched link-down status in polling mode")
Signed-off-by: Petr Oros <poros@...hat.com>
---
 drivers/net/phy/phy-c45.c    | 5 +++--
 drivers/net/phy/phy_device.c | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/net/phy/phy-c45.c b/drivers/net/phy/phy-c45.c
index a1caeee1223617..bceb0dcdecbd61 100644
--- a/drivers/net/phy/phy-c45.c
+++ b/drivers/net/phy/phy-c45.c
@@ -239,9 +239,10 @@ int genphy_c45_read_link(struct phy_device *phydev)
 
 		/* The link state is latched low so that momentary link
 		 * drops can be detected. Do not double-read the status
-		 * in polling mode to detect such short link drops.
+		 * in polling mode to detect such short link drops except
+		 * the link was already down.
 		 */
-		if (!phy_polling_mode(phydev)) {
+		if (!phy_polling_mode(phydev) || !phydev->link) {
 			val = phy_read_mmd(phydev, devad, MDIO_STAT1);
 			if (val < 0)
 				return val;
diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 6a5056e0ae7757..05417419c484fa 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1930,9 +1930,10 @@ int genphy_update_link(struct phy_device *phydev)
 
 	/* The link state is latched low so that momentary link
 	 * drops can be detected. Do not double-read the status
-	 * in polling mode to detect such short link drops.
+	 * in polling mode to detect such short link drops except
+	 * the link was already down.
 	 */
-	if (!phy_polling_mode(phydev)) {
+	if (!phy_polling_mode(phydev) || !phydev->link) {
 		status = phy_read(phydev, MII_BMSR);
 		if (status < 0)
 			return status;
-- 
2.24.1