Re: [PATCH 2/2] net: phy: Provide Module 4 KSZ9477 errata (DS80000754C)

[Lukasz Majewski]

Hi Oleksij,

> On Wed, Aug 30, 2023 at 11:21:19AM +0200, Lukasz Majewski wrote:
> > The KSZ9477 errata points out (in 'Module 4') the link up/down
> > problem when EEE (Energy Efficient Ethernet) is enabled in the
> > device to which the KSZ9477 tries to auto negotiate.
> > 
> > The suggested workaround is to clear advertisement of EEE for PHYs
> > in this chip driver.
> > 
> > Signed-off-by: Lukasz Majewski <lukma@xxxxxxx>
> > ---
> >  drivers/net/phy/micrel.c | 31 ++++++++++++++++++++++++++++++-
> >  1 file changed, 30 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
> > index 87b090ad2874..469dcd8a5711 100644
> > --- a/drivers/net/phy/micrel.c
> > +++ b/drivers/net/phy/micrel.c
> > @@ -1418,6 +1418,35 @@ static int ksz9131_get_features(struct
> > phy_device *phydev) return 0;
> >  }
> >  
> > +static int ksz9477_get_features(struct phy_device *phydev)
> > +{
> > +	__ETHTOOL_DECLARE_LINK_MODE_MASK(zero) = { 0, };
> > +	int ret;
> > +
> > +	ret = genphy_read_abilities(phydev);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* KSZ9477 Errata DS80000754C
> > +	 *
> > +	 * Module 4: Energy Efficient Ethernet (EEE) feature
> > select must be
> > +	 * manually disabled
> > +	 *   The EEE feature is enabled by default, but it is not
> > fully
> > +	 *   operational. It must be manually disabled through
> > register
> > +	 *   controls. If not disabled, the PHY ports can
> > auto-negotiate
> > +	 *   to enable EEE, and this feature can cause link drops
> > when linked
> > +	 *   to another device supporting EEE.
> > +	 *
> > +	 *   Although, the KSZ9477 MMD register
> > +	 *   (MMD_DEVICE_ID_EEE_ADV.MMD_EEE_ADV) advertise that
> > EEE is
> > +	 *   operational one needs to manualy clear them to follow
> > the chip
> > +	 *   errata.
> > +	 */
> > +	linkmode_and(phydev->supported_eee, phydev->supported,
> > zero); +
> > +	return 0;
> > +}
> > +
> >  #define KSZ8873MLL_GLOBAL_CONTROL_4	0x06
> >  #define KSZ8873MLL_GLOBAL_CONTROL_4_DUPLEX	BIT(6)
> >  #define KSZ8873MLL_GLOBAL_CONTROL_4_SPEED	BIT(4)
> > @@ -4871,7 +4900,7 @@ static struct phy_driver ksphy_driver[] = {
> >  	.handle_interrupt = kszphy_handle_interrupt,
> >  	.suspend	= genphy_suspend,
> >  	.resume		= genphy_resume,
> > -	.get_features	= ksz9131_get_features,
> > +	.get_features	= ksz9477_get_features,  
> 
> Sorry, i didn't described all details how to implement it.
> 
> This code will break EEE support for the KSZ8563R switch.
> 

And then another switch (KSZ8563R) pops up.... with regression....

In the micrel.c the ksz9477_get_features was only present in:
https://elixir.bootlin.com/linux/latest/source/drivers/net/phy/micrel.c#L4832
https://elixir.bootlin.com/linux/latest/source/drivers/net/phy/micrel.c#L4874
so I only changed it there.

Apparently the KSZ8563R re-uses the KSZ9477 code.

> Please search for MICREL_KSZ8_P1_ERRATA in the kernel source.
> Then add new flag, for example MICREL_NO_EEE and use it in a similar
> way how MICREL_KSZ8_P1_ERRATA was set and used. With this
> implementation, first patch is not needed.
> 
> The code will be something like this:
>    if (dev_flags & MICREL_NO_EEE)
>       /* lots of comments */
>       linkmode_and(phydev->supported_eee, phydev->supported, zero);
>    else
>       /* lots of other comments */
>       linkmode_and(phydev->supported_eee, phydev->supported,
>                    PHY_EEE_CAP1_FEATURES);
> 
> On the switch driver side i would expect something like this:
> ksz_get_phy_flags(struct dsa_switch *ds, int port)
> 
>        swtich (dev->chip_id)
>        case KSZ8830_CHIP_ID:
>          ....
>          break;
>        case KSZ9477_CHIP_ID:
>          return MICREL_NO_EEE;
> 

Ok.

> 
> Regards,
> Oleksij




Best regards,

Lukasz Majewski

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