From: Petr Oros poros@redhat.com
commit e96bd2d3b1f83170d1d5c1a99e439b39a22a5b58 upstream.
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.
Details about this quirky behavior on Realtek phy: Without patch: T0: aneg is started, link goes down, link-down status is latched T0+3s: state machine runs, up-to-date link-down is read T0+4s: state machine runs, aneg is finished (BMSR_ANEGCOMPLETE==1), here i read link-down (BMSR_LSTATUS==0), T0+5s: state machine runs, aneg is finished (BMSR_ANEGCOMPLETE==1), up-to-date link-up is read (BMSR_LSTATUS==1), phydev->link goes up, state change PHY_NOLINK to PHY_RUNNING
With patch: T0: aneg is started, link goes down, link-down status is latched T0+3s: state machine runs, up-to-date link-down is read T0+4s: state machine runs, aneg is finished (BMSR_ANEGCOMPLETE==1), first BMSR read: BMSR_ANEGCOMPLETE==1 and BMSR_LSTATUS==0, second BMSR read: BMSR_ANEGCOMPLETE==1 and BMSR_LSTATUS==1, phydev->link goes up, state change PHY_NOLINK to PHY_RUNNING
Signed-off-by: Petr Oros poros@redhat.com Reviewed-by: Heiner Kallweit hkallweit1@gmail.com Signed-off-by: David S. Miller davem@davemloft.net Cc: Macpaul Lin macpaul.lin@mediatek.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/phy/phy-c45.c | 5 +++-- drivers/net/phy/phy_device.c | 5 +++-- 2 files changed, 6 insertions(+), 4 deletions(-)
--- 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_devi
/* 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; --- a/drivers/net/phy/phy_device.c +++ b/drivers/net/phy/phy_device.c @@ -1766,9 +1766,10 @@ int genphy_update_link(struct phy_device
/* 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;