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

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Message-ID: <20250313095729.53a621e0@fedora-2.home>
Date: Thu, 13 Mar 2025 09:57:29 +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

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 ?

Maxime