Re: [PATCH net-next v10 3/5] net: phy: micrel: Add loopback support

Maxime Chevallier
2025-03-13T09:41:33Z

Hi,

On Thu, 13 Mar 2025 10:35:47 +0100
Gerhard Engleder <gerhard@engleder-embedded.com> wrote:

> Am 13.03.2025 09:57, schrieb Maxime Chevallier:
> > Hello Gerhard,
> >
> > On Wed, 12 Mar 2025 21:30:08 +0100
> > Gerhard Engleder <gerhard@engleder-embedded.com> wrote:
> >
> >> The KSZ9031 PHYs requires full duplex for loopback mode. Add PHY
> >> specific set_loopback() to ensure this.
> >>
> >> Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
> >> ---
> >> drivers/net/phy/micrel.c | 24 ++++++++++++++++++++++++
> >> 1 file changed, 24 insertions(+)
> >>
> >> diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
> >> index 289e1d56aa65..24882d30f685 100644
> >> --- a/drivers/net/phy/micrel.c
> >> +++ b/drivers/net/phy/micrel.c
> >> @@ -1032,6 +1032,29 @@ static int ksz9021_config_init(struct
> >> phy_device *phydev)
> >> #define MII_KSZ9031RN_EDPD 0x23
> >> #define MII_KSZ9031RN_EDPD_ENABLE BIT(0)
> >>
> >> +static int ksz9031_set_loopback(struct phy_device *phydev, bool
> >> enable,
> >> + int speed)
> >> +{
> >> + u16 ctl = BMCR_LOOPBACK;
> >> + int val;
> >> +
> >> + if (!enable)
> >> + return genphy_loopback(phydev, enable, 0);
> >> +
> >> + if (speed == SPEED_10 || speed == SPEED_100 || speed == SPEED_1000)
> >> + phydev->speed = speed;
> >> + else if (speed)
> >> + return -EINVAL;
> >> + phydev->duplex = DUPLEX_FULL;
> >> +
> >> + ctl |= mii_bmcr_encode_fixed(phydev->speed, phydev->duplex);
> >> +
> >> + phy_write(phydev, MII_BMCR, ctl);
> >> +
> >> + return phy_read_poll_timeout(phydev, MII_BMSR, val, val &
> >> BMSR_LSTATUS,
> >> + 5000, 500000, true);
> >
> > Maybe I don't fully get it, but it looks to me that you poll, waiting
> > for the link to become up. As you are in local loopback mode, how does
> > that work ? Do you need connection to an active LP for loopback to
> > work, or does the BMSR_LSTATUS bit behave differently under local
> > loopback ?
>
> Yes I'm polling for link to come up. This is identical to
> genphy_loopback().
> There is no need for a link partner to get a link up in loopback mode.
> BMSR_LSTATUS reflects the loopback as link in this case.
>
> This series allows to configure a loopback with defined speed without
> any
> link partner. Currently for PHY loopback a link partner is needed in
> some
> cases (starting with 1 Gbps loopback).

Ok thanks a lot for the clarification ! It looks good to me in that
case :)

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Maxime