Re: [PATCH net] net: phy: dp83869: Set auto mdix bit for forced 100Base-Tx mode

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

Hi Meghana,

On 12/02/2026 07:21, Meghana Malladi wrote:
> Hi Andrew,
> 
> On 2/11/26 19:42, Andrew Lunn wrote:
>> On Wed, Feb 11, 2026 at 06:40:32PM +0530, Meghana Malladi wrote:
>>> When using DP83869 in force 100Base-Tx mode, the PHY is required
>>> to have robust Auto-MDIX feature enabled from register 1Eh.
>>> Refer to 7.4.1.2 100BASE-TX section in the TRM [1] for more details.
>>
>> What are the results of not enabling this? How would somebody know
>> they need this patch?
> 
> This is the fix for 100M full duplex when auto-neg gets disabled, it 
> fails to have a link up and this patch fixes it. I will add more 
> description to the commit message.

I have a board here with a DP83869 + imx93's dwmac, but I couldn't
trigger the bug locally. I forced speed, dpx and aneg settings with :

ethtool -s eth0 speed 100 duplex full autoneg off

I did the same on the link partner, but I was still able to get link-up.

I'm not saying the bug isn't real, I mostly curious about the kind of
circumstances that causes this prblem to show-up. Do you have any
clarifications on that ?

I'll be happy to give the fix a try, if I can manage to reproduce the
issue :)

Maxime