On Sun, May 31, 2020 at 12:43:15AM +0300, Vladimir Oltean wrote:
From: Vladimir Oltean vladimir.oltean@nxp.com
In kernel 4.19 (and probably earlier too) there are issues surrounding the PHY_AN state.
For example, if a PHY is in PHY_AN state and AN has not finished, then what is supposed to happen is that the state machine gets rescheduled until it is, or until the link_timeout reaches zero which triggers an autoneg restart process.
But actually the rescheduling never works if the PHY uses interrupts, because the condition under which rescheduling occurs is just if phy_polling_mode() is true. So basically, this whole rescheduling functionality works for AN-not-yet-complete just by mistake. Let me explain.
Most of the time the AN process manages to finish by the time the interrupt has triggered. One might say "that should always be the case, otherwise the PHY wouldn't raise the interrupt, right?". Well, some PHYs implement an .aneg_done method which allows them to tell the state machine when the AN is really complete. The AR8031/AR8033 driver (at803x.c) is one such example. Even when copper autoneg completes, the driver still keeps the "aneg_done" variable unset until in-band SGMII autoneg finishes too (there is no interrupt for that). So we have the premises of a race condition.
Why do we care whether SGMII autoneg has completed - is that not the domain of the MAC side of the link?
It sounds like things are a little confused. The PHY interrupt is signalling that the copper side has completed its autoneg. If we're in SGMII mode, the PHY can now start the process of informing the MAC about the negotiation results across the SGMII link. When the MAC receives those results, and sends the acknowledgement back to the PHY, is it not the responsibility of the MAC to then say "the link is now up" ?
That's how we deal with it elsewhere with phylink integration, which is what has to be done when you have to cope with PHYs that switch their host interface mode between SGMII, 2500BASE-X, 5GBASE-R and 10GBASE-R - the MAC side needs to be dynamically reconfigured depending on the new host-side operating mode of the PHY. Only when the MAC subsequently reports that the link has been established is the whole link from the MAC to the media deemed to be operational.