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

Gerhard Engleder
2025-03-13T10:30:35Z

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).

Gerhard