Am 24.11.2020 um 15:38 schrieb Antonio Borneo:
> If the auto-negotiation fails to establish a gigabit link, the phy
> can try to 'down-shift': it resets the bits in MII_CTRL1000 to
> stop advertising 1Gbps and retries the negotiation at 100Mbps.
>
I see that Russell answered already. My 2cts:
Are you sure all PHY's supporting downshift adjust the
advertisement bits? IIRC an Aquantia PHY I dealt with does not.
And if a PHY does so I'd consider this problematic:
Let's say you have a broken cable and the PHY downshifts to
100Mbps. If you change the cable then the PHY would still negotiate
100Mbps only.
Also I think phydev->advertising reflects what the user wants to
advertise, as mentioned by Russell before.
>>From commit 5502b218e001 ("net: phy: use phy_resolve_aneg_linkmode
> in genphy_read_status") the content of MII_CTRL1000 is not checked
> anymore at the end of the negotiation, preventing the detection of
> phy 'down-shift'.
> In case of 'down-shift' phydev->advertising gets out-of-sync wrt
> MII_CTRL1000 and still includes modes that the phy have already
> dropped. The link partner could still advertise higher speeds,
> while the link is established at one of the common lower speeds.
> The logic 'and' in phy_resolve_aneg_linkmode() between
> phydev->advertising and phydev->lp_advertising will report an
> incorrect mode.
>
> Issue detected with a local phy rtl8211f connected with a gigabit
> capable router through a two-pairs network cable.
>
> After auto-negotiation, read back MII_CTRL1000 and mask-out from
> phydev->advertising the modes that have been eventually discarded
> due to the 'down-shift'.
>
> Fixes: 5502b218e001 ("net: phy: use phy_resolve_aneg_linkmode in genphy_read_status")
> Cc: stable@xxxxxxxxxxxxxxx # v5.1+
> Signed-off-by: Antonio Borneo <antonio.borneo@xxxxxx>
> Link: https://lore.kernel.org/r/478f871a-583d-01f1-9cc5-2eea56d8c2a7@xxxxxxxxxx
> ---
> To: Andrew Lunn <andrew@xxxxxxx>
> To: Heiner Kallweit <hkallweit1@xxxxxxxxx>
> To: Russell King <linux@xxxxxxxxxxxxxxx>
> To: "David S. Miller" <davem@xxxxxxxxxxxxx>
> To: Jakub Kicinski <kuba@xxxxxxxxxx>
> To: netdev@xxxxxxxxxxxxxxx
> To: Yonglong Liu <liuyonglong@xxxxxxxxxx>
> Cc: linuxarm@xxxxxxxxxx
> Cc: Salil Mehta <salil.mehta@xxxxxxxxxx>
> Cc: linux-stm32@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: Antonio Borneo <antonio.borneo@xxxxxx>
>
> drivers/net/phy/phy_device.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 5dab6be6fc38..5d1060aa1b25 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -2331,7 +2331,7 @@ EXPORT_SYMBOL(genphy_read_status_fixed);
> */
> int genphy_read_status(struct phy_device *phydev)
> {
> - int err, old_link = phydev->link;
> + int adv, err, old_link = phydev->link;
>
> /* Update the link, but return if there was an error */
> err = genphy_update_link(phydev);
> @@ -2356,6 +2356,14 @@ int genphy_read_status(struct phy_device *phydev)
> return err;
>
> if (phydev->autoneg == AUTONEG_ENABLE && phydev->autoneg_complete) {
> + if (phydev->is_gigabit_capable) {
> + adv = phy_read(phydev, MII_CTRL1000);
> + if (adv < 0)
> + return adv;
> + /* update advertising in case of 'down-shift' */
> + mii_ctrl1000_mod_linkmode_adv_t(phydev->advertising,
> + adv);
> + }
> phy_resolve_aneg_linkmode(phydev);
> } else if (phydev->autoneg == AUTONEG_DISABLE) {
> err = genphy_read_status_fixed(phydev);
>
> base-commit: d549699048b4b5c22dd710455bcdb76966e55aa3
>
