Re: [RFC PATCH net] net: phy: Fix "link partner" information disappear issue

[Heiner Kallweit <hkallweit1@gmail.com>]

On 10.10.2019 11:30, Yonglong Liu wrote:
> Some drivers just call phy_ethtool_ksettings_set() to set the
> links, for those phy drivers that use genphy_read_status(), if
> autoneg is on, and the link is up, than execute "ethtool -s
> ethx autoneg on" will cause "link partner" information disappear.
> 
> The call trace is phy_ethtool_ksettings_set()->phy_start_aneg()
> ->linkmode_zero(phydev->lp_advertising)->genphy_read_status(),
> the link didn't change, so genphy_read_status() just return, and
> phydev->lp_advertising is zero now.
> 
I think that clearing link partner advertising info in
phy_start_aneg() is questionable. If advertising doesn't change
then phy_config_aneg() basically is a no-op. Instead we may have
to clear the link partner advertising info in genphy_read_lpa()
if aneg is disabled or aneg isn't completed (basically the same
as in genphy_c45_read_lpa()). Something like:

if (!phydev->autoneg_complete) { /* also covers case that aneg is disabled */
	linkmode_zero(phydev->lp_advertising);
} else if (phydev->autoneg == AUTONEG_ENABLE) {
	...
}

> This patch call genphy_read_lpa() before the link state judgement
> to fix this problem.
> 
> Fixes: 88d6272acaaa ("net: phy: avoid unneeded MDIO reads in genphy_read_status")
> Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
> ---
>  drivers/net/phy/phy_device.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 9d2bbb1..ef3073c 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -1839,6 +1839,10 @@ int genphy_read_status(struct phy_device *phydev)
>  	if (err)
>  		return err;
>  
> +	err = genphy_read_lpa(phydev);
> +	if (err < 0)
> +		return err;
> +
>  	/* why bother the PHY if nothing can have changed */
>  	if (phydev->autoneg == AUTONEG_ENABLE && old_link && phydev->link)
>  		return 0;
> @@ -1848,10 +1852,6 @@ int genphy_read_status(struct phy_device *phydev)
>  	phydev->pause = 0;
>  	phydev->asym_pause = 0;
>  
> -	err = genphy_read_lpa(phydev);
> -	if (err < 0)
> -		return err;
> -
>  	if (phydev->autoneg == AUTONEG_ENABLE && phydev->autoneg_complete) {
>  		phy_resolve_aneg_linkmode(phydev);
>  	} else if (phydev->autoneg == AUTONEG_DISABLE) {
>