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

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Message-ID: <20250313104128.3f6cb9e3@fedora-2.home>
Date: Thu, 13 Mar 2025 10:41:28 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Gerhard Engleder <gerhard@...leder-embedded.com>
Cc: andrew@...n.ch, hkallweit1@...il.com, linux@...linux.org.uk,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v10 3/5] net: phy: micrel: Add loopback support

Hi,

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

Maxime