Re: [PATCH v2] net: usb: lan78xx: scan all MDIO addresses on LAN7801

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi Martin,

On 16/02/2026 06:09, Martin Pålsson wrote:
> The LAN7801 is designed exclusively for external PHYs (unlike the
> LAN7800/LAN7850 which have internal PHYs), but lan78xx_mdio_init()
> restricts PHY scanning to MDIO addresses 0-7 by setting phy_mask to
> ~(0xFF). This prevents discovery of external PHYs wired to addresses
> outside that range.
> 
> One such case is the DP83TC814 100BASE-T1 PHY, which is typically
> configured at MDIO address 10 via PHYAD bootstrap pins and goes
> undetected with the current mask.
> 
> Set phy_mask to 0 for the LAN7801 so that all 32 MDIO addresses are
> scanned during bus registration, allowing any external PHY to be
> discovered regardless of its address.
> 
> Fixes: 02dc1f3d613d ("lan78xx: add LAN7801 MAC only support")
> 
> Signed-off-by: Martin Pålsson <martin@poleshift.se>
> ---
> Changes in v2:
> - Added Fixes: tag
> - Link to v1: https://lore.kernel.org/r/20260214-lan78xx-phy-mask-fix-v1-1-3baa100861e4@poleshift.se
> ---
>  drivers/net/usb/lan78xx.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
> index 00397a807393..9d8f1ff7028d 100644
> --- a/drivers/net/usb/lan78xx.c
> +++ b/drivers/net/usb/lan78xx.c
> @@ -2094,8 +2094,8 @@ static int lan78xx_mdio_init(struct lan78xx_net *dev)
>  		dev->mdiobus->phy_mask = ~(1 << 1);
>  		break;
>  	case ID_REV_CHIP_ID_7801_:
> -		/* scan thru PHYAD[2..0] */
> -		dev->mdiobus->phy_mask = ~(0xFF);
> +		/* scan all 32 MDIO addresses for external PHYs */
> +		dev->mdiobus->phy_mask = 0;

As this is the default behaviour for mdio bus controllers, and the
default value for the mask is 0, I think you can simply discard that
assignment.

I don't even think we need a comment, as the other cases for 7800/7850
already have a comment explaining why they are special cases.

Maxime