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

[Malladi, Meghana]

Hi Maxime,

On 2/13/2026 12:10 AM, Maxime Chevallier wrote:
> 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
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> 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.

Your steps so far are correct. But I didn't do the same settings on the 
link partner. With other speeds (10M, 1G) I was seeing a link up without 
the need to force speed on the link partner side. So I was expecting the 
same with 100M as well.

> 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 ?

Also when I tried the same between DP83869 PHYs of two AM64x (TI DUTs) I 
couldn't see this issue. When I tried between DP83869 PHY and an 
external switch or PC I was able to reproduce this issue.

May be I missing lot of detail in this patch. Let me know if this helped 
you with reproducing the issue. Thanks a lot :)

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

--
Thanks,
Meghana Malladi